It is not "in bytes" for wide char literal.

* Use FL_USER0 for ELTS_SHARED

This makes space in RString for two bits for chilled strings.

* Mark strings returned by `Symbol#to_s` as chilled

[Feature #20350]

`STR_CHILLED` now spans on two user flags. If one bit is set it
marks a chilled string literal, if it's the other it marks a
`Symbol#to_s` chilled string.

Since it's not possible, and doesn't make much sense to include
debug info when `--debug-frozen-string-literal` is set, we can't
include allocation source, but we can safely include the symbol
name in the warning message, making it much easier to find the source
of the issue.

Co-Authored-By: Étienne Barrié <etienne.barrie@gmail.com>

---------

Co-authored-by: Étienne Barrié <etienne.barrie@gmail.com>
Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

If `long` and `int` are the same size, `unsigned int` max would exceed
`signed long` range.  It is guaranteed by `RB_POSFIXABLE` that `v` can
be casted to `long` safely here.

Since 730e3b2ce01915c4a98b79bb281b2c38a9ff1131
("Stop exposing `rb_str_chilled_p`"), we noticed a speed loss on a few
benchmarks that are string operations heavy. This is partially due to
routines no longer having the options to inline rb_check_frozen_inline()
in non-LTO builds. Make it an inlining candidate again to recover speed.

Testing this patch on my machine, the fannkuchredux benchmark gets a
1.15 speed-up with YJIT and 1.03 without YJIT.

[Feature #20589]

[Feature #20205]

Now that chilled strings no longer appear as frozen, there is no
need to offer an API to check for chilled strings.

We however need to change `rb_check_frozen_internal` to no
longer be a macro, as it needs to check for chilled strings.

They were initially made frozen to avoid false positives for cases such
as:

    str = str.dup if str.frozen?

But this may cause bugs and is generally confusing for users.

[Feature #20205]

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>