These must not be changed once initialized.

* Refactor Regexp#match cache implementation

Improved variable and function names
Fixed [Bug 19537] (Maybe fixed in https://github.com/ruby/ruby/pull/7694)

* Add a comment of the glossary for "match cache"

* Skip to reset match cache when no cache point on null check

Followup: ac123f167a364c3d7a43eca78d564e41f6dbb91e

RB_WARN_CATEGORY_ALL_BITS is exposed in a public header, so it
makes sense for it to be updated to contain all valid bits.

Instead we introduce RB_WARN_CATEGORY_DEFAULT_BITS to list the
categories that are enabled by default.

[Feature #19538]

This new `peformance` warning category is disabled by default.
It needs to be specifically enabled via `-W:performance` or `Warning[:performance] = true`

Remove !USE_RVARGC code

[Feature #19579]

The Variable Width Allocation feature was turned on by default in Ruby
3.2. Since then, we haven't received bug reports or backports to the
non-Variable Width Allocation code paths, so we assume that nobody is
using it. We also don't plan on maintaining the non-Variable Width
Allocation code, so we are going to remove it.

* Skip test if non-blocking file IO is not supported.

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>