Use an st table for "too complex" objects

	st tables will maintain insertion order so we can marshal dump / load
	objects with instance variables in the same order they were set on that
	particular instance

	[ruby-core:112926] [Bug #19535]

	Co-Authored-By: Jemma Issroff <jemmaissroff@gmail.com>
	---
	 gc.c                     | 10 ++++------
	 include/ruby/st.h        |  2 ++
	 object.c                 |  2 +-
	 ractor.c                 | 43 ++++++++++++++++++++++---------------------
	 shape.h                  |  6 +++---
	 st.c                     |  6 ++++++
	 test/ruby/test_shapes.rb | 21 +++++++++++++++++++++
	 variable.c               | 28 ++++++++++++++--------------
	 vm_insnhelper.c          |  2 +-
	 9 files changed, 74 insertions(+), 46 deletions(-)

	[Bug #19289] Retain `ruby_abi_version` function

	A few extension libraries, to hide all symbols except for necessary to
	load, hardcode the symbols to be exported in symbol list files for
	linker without even checking by `have_func`.  As a workaround for such
	libraries, retain `ruby_abi_version` symbol always even in released
	versions for now.
	---
	 include/ruby/internal/abi.h | 7 +++++--
	 1 file changed, 5 insertions(+), 2 deletions(-)

* See https://bugs.ruby-lang.org/issues/19078#note-30

The documentation says that the `end` pointer will be marked
but looking at the source, that is not the case.

Although the storage of the opaque Ruby object is an array of VALUEs, the intention of RB_ALLOCV is to allocate bytes of memory.

* Slightly more consistent indentation with other parts of the document.