String#bytesplice should return self

	In Feature #19314, we concluded that the return value of String#bytesplice
	should be changed from the source string to the receiver, because the source
	string is useless and confusing when extra arguments are added.

	This change should be included in Ruby 3.2.1.
	---
	 string.c                 | 4 ++--
	 test/ruby/test_string.rb | 2 +-
	 2 files changed, 3 insertions(+), 3 deletions(-)

Calling `String#scan` without a block creates an incomplete MatchData
object whose `RMATCH(match)->str` is Qfalse. Usually this object is not
leaked, but it was possible to pull it by using ObjectSpace.each_object.

This change hides the internal MatchData object by using rb_obj_hide.

Fixes [Bug #19159]

It's questionable whether we want to allow rstrip to work for strings
where the broken coderange occurs before the trailing whitespace and
not after, but this approach is probably simpler, and I don't think
users should expect string operations like rstrip to work on broken
strings.

In some cases, this changes rstrip to raise
Encoding::CompatibilityError instead of ArgumentError.  However, as
the problem is related to an encoding issue in the receiver, and due
not due to an issue with an argument, I think
Encoding::CompatibilityError is the more appropriate error.

Fixes [Bug #18931]

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

This is an inelegant hack, by manually checking for this specific
code point in rb_str_inspect.  Some testing indicates that this is
the only code point affected.

It's possible a better fix would be inside of lower-level encoding
code, such that rb_enc_isprint would return false and not true for
codepoint 0x85.

Fixes [Bug #16842]

Previously, it was including one newline when chomp was used,
which is inconsistent with IO#each_line behavior. This makes
behavior consistent with IO#each_line, chomping all paragraph
separators (multiple consecutive newlines), but not single
newlines.

Partially Fixes [Bug #18768]

* Add String#byteindex, String#byterindex, and MatchData#byteoffset [Feature #13110]

Co-authored-by: NARUSE, Yui <naruse@airemix.jp>