Fix Visual C warnings:
```
iseq.c(3793): warning C4312: 'type cast': conversion from 'int' to 'void *' of greater size
iseq.c(3794): warning C4312: 'type cast': conversion from 'int' to 'void *' of greater size
```

	Push a real iseq in rb_vm_push_frame_fname()

	Previously, vm_make_env_each() (used during proc
	creation and for the debug inspector C API) picked up the
	non-GC-allocated iseq that rb_vm_push_frame_fname() creates,
	which led to a SEGV when the GC tried to mark the non GC object.

	Put a real iseq imemo instead. Speed should be about the same since
	the old code also did a imemo allocation and a malloc allocation.

	Real iseq allows ironing out the special-casing of dummy frames in
	rb_execution_context_mark() and rb_execution_context_update(). A check
	is added to RubyVM::ISeq#eval, though, to stop attempts to run dummy
	iseqs.

	[Bug #21180]

	Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

	Fix use-after-free in constant cache

	[Bug #20921]

	When we create a cache entry for a constant, the following sequence of
	events could happen:

	- vm_track_constant_cache is called to insert a constant cache.
	- In vm_track_constant_cache, we first look up the ST table for the ID
	  of the constant. Assume the ST table exists because another iseq also
	  holds a cache entry for this ID.
	- We then insert into this ST table with the iseq_inline_constant_cache.
	- However, while inserting into this ST table, it allocates memory, which
	  could trigger a GC. Assume that it does trigger a GC.
	- The GC frees the one and only other iseq that holds a cache entry for
	  this ID.
	- In remove_from_constant_cache, it will appear that the ST table is now
	  empty because there are no more iseq with cache entries for this ID, so
	  we free the ST table.
	- We complete GC and continue our st_insert. However, this ST table has
	  been freed so we now have a use-after-free.

	This issue is very hard to reproduce, because it requires that the GC runs
	at a very specific time. However, we can make it show up by applying this
	patch which runs GC right before the st_insert to mimic the st_insert
	triggering a GC:

	    diff --git a/vm_insnhelper.c b/vm_insnhelper.c
	    index 3cb23f06f0..a93998136a 100644
	    --- a/vm_insnhelper.c
	    +++ b/vm_insnhelper.c
	    @@ -6338,6 +6338,10 @@ vm_track_constant_cache(ID id, void *ic)
	            rb_id_table_insert(const_cache, id, (VALUE)ics);
	        }

	    +    if (id == rb_intern("MyConstant")) rb_gc();
	    +
	        st_insert(ics, (st_data_t) ic, (st_data_t) Qtrue);
	    }

	And if we run this script:

	    Object.const_set("MyConstant", "Hello!")

	    my_proc = eval("-> { MyConstant }")
	    my_proc.call

	    my_proc = eval("-> { MyConstant }")
	    my_proc.call

	We can see that ASAN outputs a use-after-free error:

	    ==36540==ERROR: AddressSanitizer: heap-use-after-free on address 0x606000049528 at pc 0x000102f3ceac bp 0x00016d607a70 sp 0x00016d607a68
	    READ of size 8 at 0x606000049528 thread T0
	        #0 0x102f3cea8 in do_hash st.c:321
	        #1 0x102f3ddd0 in rb_st_insert st.c:1132
	        #2 0x103140700 in vm_track_constant_cache vm_insnhelper.c:6345
	        #3 0x1030b91d8 in vm_ic_track_const_chain vm_insnhelper.c:6356
	        #4 0x1030b8cf8 in rb_vm_opt_getconstant_path vm_insnhelper.c:6424
	        #5 0x1030bc1e0 in vm_exec_core insns.def:263
	        #6 0x1030b55fc in rb_vm_exec vm.c:2585
	        #7 0x1030fe0ac in rb_iseq_eval_main vm.c:2851
	        #8 0x102a82588 in rb_ec_exec_node eval.c:281
	        #9 0x102a81fe0 in ruby_run_node eval.c:319
	        #10 0x1027f3db4 in rb_main main.c:43
	        #11 0x1027f3bd4 in main main.c:68
	        #12 0x183900270  (<unknown module>)

	    0x606000049528 is located 8 bytes inside of 56-byte region [0x606000049520,0x606000049558)
	    freed by thread T0 here:
	        #0 0x104174d40 in free+0x98 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x54d40)
	        #1 0x102ada89c in rb_gc_impl_free default.c:8183
	        #2 0x102ada7dc in ruby_sized_xfree gc.c:4507
	        #3 0x102ac4d34 in ruby_xfree gc.c:4518
	        #4 0x102f3cb34 in rb_st_free_table st.c:663
	        #5 0x102bd52d8 in remove_from_constant_cache iseq.c:119
	        #6 0x102bbe2cc in iseq_clear_ic_references iseq.c:153
	        #7 0x102bbd2a0 in rb_iseq_free iseq.c:166
	        #8 0x102b32ed0 in rb_imemo_free imemo.c:564
	        #9 0x102ac4b44 in rb_gc_obj_free gc.c:1407
	        #10 0x102af4290 in gc_sweep_plane default.c:3546
	        #11 0x102af3bdc in gc_sweep_page default.c:3634
	        #12 0x102aeb140 in gc_sweep_step default.c:3906
	        #13 0x102aeadf0 in gc_sweep_rest default.c:3978
	        #14 0x102ae4714 in gc_sweep default.c:4155
	        #15 0x102af8474 in gc_start default.c:6484
	        #16 0x102afbe30 in garbage_collect default.c:6363
	        #17 0x102ad37f0 in rb_gc_impl_start default.c:6816
	        #18 0x102ad3634 in rb_gc gc.c:3624
	        #19 0x1031406ec in vm_track_constant_cache vm_insnhelper.c:6342
	        #20 0x1030b91d8 in vm_ic_track_const_chain vm_insnhelper.c:6356
	        #21 0x1030b8cf8 in rb_vm_opt_getconstant_path vm_insnhelper.c:6424
	        #22 0x1030bc1e0 in vm_exec_core insns.def:263
	        #23 0x1030b55fc in rb_vm_exec vm.c:2585
	        #24 0x1030fe0ac in rb_iseq_eval_main vm.c:2851
	        #25 0x102a82588 in rb_ec_exec_node eval.c:281
	        #26 0x102a81fe0 in ruby_run_node eval.c:319
	        #27 0x1027f3db4 in rb_main main.c:43
	        #28 0x1027f3bd4 in main main.c:68
	        #29 0x183900270  (<unknown module>)

	    previously allocated by thread T0 here:
	        #0 0x104174c04 in malloc+0x94 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x54c04)
	        #1 0x102ada0ec in rb_gc_impl_malloc default.c:8198
	        #2 0x102acee44 in ruby_xmalloc gc.c:4438
	        #3 0x102f3c85c in rb_st_init_table_with_size st.c:571
	        #4 0x102f3c900 in rb_st_init_table st.c:600
	        #5 0x102f3c920 in rb_st_init_numtable st.c:608
	        #6 0x103140698 in vm_track_constant_cache vm_insnhelper.c:6337
	        #7 0x1030b91d8 in vm_ic_track_const_chain vm_insnhelper.c:6356
	        #8 0x1030b8cf8 in rb_vm_opt_getconstant_path vm_insnhelper.c:6424
	        #9 0x1030bc1e0 in vm_exec_core insns.def:263
	        #10 0x1030b55fc in rb_vm_exec vm.c:2585
	        #11 0x1030fe0ac in rb_iseq_eval_main vm.c:2851
	        #12 0x102a82588 in rb_ec_exec_node eval.c:281
	        #13 0x102a81fe0 in ruby_run_node eval.c:319
	        #14 0x1027f3db4 in rb_main main.c:43
	        #15 0x1027f3bd4 in main main.c:68
	        #16 0x183900270  (<unknown module>)

	This commit fixes this bug by adding a inserting_constant_cache_id field
	to the VM, which stores the ID that is currently being inserted and, in
	remove_from_constant_cache, we don't free the ST table for ID equal to
	this one.

	Co-Authored-By: Alan Wu <alanwu@ruby-lang.org>

	fix iseq kwargs table and original_iseq leaks

	[bug #19903]

	Co-authored-by: Peter Zhu <peter@peterzhu.ca>
	---
	 iseq.c | 4 ++++
	 1 file changed, 4 insertions(+)

	Ensure main file has default coverage if required. (#7169)

	* Extract common code for coverage setup.
	---
	 iseq.c | 13 +++++++++++--
	 1 file changed, 11 insertions(+), 2 deletions(-)

	More coverage tests & specs. (#7171)

	* Add spec for eval and line coverage.

	* Add test for main file coverage.
	---
	 spec/ruby/library/coverage/start_spec.rb | 8 +++++++-
	 test/coverage/autostart.rb               | 2 ++
	 test/coverage/main.rb                    | 1 +
	 test/coverage/test_coverage.rb           | 7 +++++++
	 4 files changed, 17 insertions(+), 1 deletion(-)
	 create mode 100644 test/coverage/autostart.rb
	 create mode 100644 test/coverage/main.rb

With this change, we're storing the iv name on an inline cache on
setinstancevariable instructions. This allows us to check the inline
cache to count instance variables set in initialize and give us an
estimate of iv capacity for an object.

For the purpose of estimating the number of instance variables required
for an object, we're assuming that all initialize methods will call
`super`.

This change allows us to estimate the number of instance variables
required without disassembling instruction sequences.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

Commit dba61f4 fixes a crash when GC'ing a iseq that failed to compile.
However, if we turn on RGENGC_CHECK_MODE then rb_iseq_memsize crashes
since it cannot handle an iseq without is_entries.

If there is a compilation error, is_entries may not be allocated, but
ic_size could be greater than 0.  If we don't have a buffer to iterate
over, just return early.  Otherwise GC could segv

[Bug #19173]

We need to make sure the name table is freed otherwise we have a memory
leak.