Fix PCRE2 Regex with more than 127 named capture groups

[HertzDevil]

Different things can happen when a Regex backed by PCRE2 has too many named capture groups:

• The 256th named capture and onward will overwrite older ones in Regex#name_table;
• The 256th named capture and onward will show up in Regex::MatchData#captures;
• Regex::MatchData#named_captures raises OverflowError when there are 128 or more named captures.

Also fixes #13347. Note that the upper limit is 10000 in both PCRE and PCRE2.

[HertzDevil]

It seems there is some kind of out-of-memory error in wasm32-test. Also for some reason it still uses PCRE instead of PCRE2