Addressed some suggestions from clippy that made sense to me.

* YJIT: Use fully-qualified name for OPTIONS in get_options!

* YJIT: Only enable disassembly colors for tty

* YJIT: Local variable register allocation

* locals are not stack temps

* Rename RegTemps to RegMappings

* Rename RegMapping to RegOpnd

* Rename local_size to num_locals

* s/stack value/operand/

* Rename spill_temps() to spill_regs()

* Clarify when num_locals becomes None

* Mention that InsnOut uses different registers

* Rename get_reg_mapping to get_reg_opnd

* Resurrect --yjit-temp-regs capability

* Use MAX_CTX_TEMPS and MAX_CTX_LOCALS

Mostly putting angle brackets around links to follow markdown syntax.

We've long had a size restriction on the code memory region such that a
u32 could refer to everything. This commit capitalizes on this
restriction by shrinking the size of `CodePtr` to be 4 bytes from 8.

To derive a full raw pointer from a `CodePtr`, one needs a base pointer.
Both `CodeBlock` and `VirtualMemory` can be used for this purpose. The
base pointer is readily available everywhere, except for in the case of
the `jit_return` "branch". Generalize lea_label() to lea_jump_target()
in the IR to delay deriving the `jit_return` address until `compile()`,
when the base pointer is available.

On railsbench, this yields roughly a 1% reduction to `yjit_alloc_size`
(58,397,765 to 57,742,248).

So that we get a reminder to check CodeBlock::has_dropped_bytes().
Internally, asm.compile() already checks it, and this patch just
propagates it out to the caller with a `#[must_use]`.

Code GC logic moved out one level in entry_stub_hit(), so the body
can freely use `?`

Co-authored-by: Alan Wu <alansi.xingwu@shopify.com>

* YJIT: Introduce Target::SideExit

* YJIT: Obviate Insn::SideExitContext

* YJIT: Avoid cloning a Context for each insn

* YJIT: Let Assembler own Context

* Update a comment

Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com>

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Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com>