Co-authored-by: Alan Wu <alanwu@ruby-lang.org>

* ZJIT: Share more code with YJIT in jit.c

* Fix ZJIT references to JIT

Addressed some suggestions from clippy that made sense to me.

Previously, `asm.mov(m32, imm32)` panicked when `imm32 > 0x80000000`. It
attempted to split imm32 into a register before doing the store, but
then the register size didn't match the destination size.

Instead of splitting, use the `MOV r/m32, imm32` form which works for
all 32-bit values. Adjust asserts that assumed that all forms undergo
sign extension, which is not true for this case.

See: 54edc930f9f0a658da45cfcef46648d1b6f82467

With a well-timed OOM around a page switch in the backend, it can return
RetryOnNextPage twice and crash due to the assert. (More places can
signal OOM now since VirtualMem tracks Rust malloc heap size for
--yjit-mem-size.)

Return error in these cases instead of crashing.

Fixes: https://github.com/Shopify/ruby/issues/566

* YJIT: Spill/load argument registers to reuse blocks

* Mention the immediate function name

* Explain the context behind spill/load operations

* YJIT: Pass method arguments using registers

* s/at_current_insn/at_compile_target/

* Implement register shuffle