Shape tree pollution could cause this test to flake.

Defining ivars in initialize method guarantees the object to be embedded.

Make Kernel#inspect ask which instance variables should be dumped by
the result of `#instance_variables_to_inspect`.

Co-Authored-By: Jean Boussier <byroot@ruby-lang.org>

[Feature #20912]

This commit ensures warnings about `object_id` and `__send__` method
redefinitions are emitted for other method types such as aliases, procs,
and attr readers—anything except C functions.

[Feature #16495]

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.

[Feature #19538]

Since that category is not enabled by default, making it a
verbose warning is redundant. Enabling performance warning should
work with the default verbosity level.