Do not emit shape transition warnings when YJIT is compiling

[Bug #20522]

If `Warning.warn` is redefined in Ruby, emitting a warning would invoke
Ruby code, which can't safely be done when YJIT is compiling.

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>
Co-authored-by: Takashi Kokubun <takashikkbn@gmail.com>

Handle mmap failures for redblack tree cache

The redblack tree cache is totally optional, so if we can't allocate
room for the cache, then just pretend as if the cache is full if mmap
fails

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

This is more consistent with other messages.

As suggested by Mame, we should try to help users fix the issues
without having to lookup the meaning of the warning.

Objects with the same shape must always have the same "embeddedness"
(either embedded or heap allocated) because YJIT assumes so. However,
using remove_instance_variable, it's possible that some objects are
embedded and some are heap allocated because it does not re-embed heap
allocated objects.

This commit changes remove_instance_variable to re-embed Object
instance variables when it becomes small enough.

The bug in i686 was fixed in commit
71babe5536bdb2238509752d8706194ee57ff485.