bug#47264: [PATCH v2] pcre: migrate to pcre2

[Carlo Marcelo Arenas Belón]

Sadly, hadn't been able to generate a release, so testing is somehow
limited to platforms where I can hack a bootstrap (macOS / a few Linux),
but it seems to be ready for some broader testing, specially if the
attached patch is applied on top of a 10.37 release (tested that way
in OpenBSD i386)

Changes since v1:
Resolved:
* Most of the suggested changes by Paul
* no more version restrictions (should work with >~10.20)
* BUG in handling of malformed UTF-8 for PCRE2 < 10.34
Pending:
* what to do with the current support of \C (enabled for now)
* merge of non critical bugfix in #51710[1]

Carlo

[1] https://debbugs.gnu.org/cgi/bugreport.cgi?bug=51710

v2-0001-pcre-migrate-to-pcre2.patch
Description: Text document