Fix RegExp UTF-16 Matching

[lemueldls]

The crate used to evaluate regexp, regress, fixed the utf-16 matching problems in their 0.10.3 release.

The RegExp::exec function now correctly matches using utf-16 instead of utf-8.

Before (main):

After (regexp-utf16):

Expected:

[kaleidawave]

Awesome! Will look at merging next week.

[kaleidawave]

PR looks good (CI red unrelated). Nice to be more correct, good to see regress supports this. Thanks for cross-referencing the behaviour in runtimes.