Drop vendored convenience copy of pcre2 #8355
Description
Ever since we've been using pcre2 as the regex backend for string, we've been shipping a vendored copy so people don't have to install it.
We've not been fantastic at keeping this up-to-date - we ship 10.36, the current is 10.38, released about 2 weeks ago. Updating it requires a procedure we've been calling "pcrectomy": https://github.com/fish-shell/fish-shell/wiki/PCREctomy. This is because we don't want to ship a bunch of files not needed by us in the source tarball.
I would like to reconsider (#2985) dropping this copy.
Now, this depends of course on the idea that installing pcre2 isn't a huge burden - distro packages will depend on it anyway (because they don't want to use the vendored copy), some systems even have it preinstalled (e.g. arch has it as a dependency of systemd, their sole supported init system!).
It would be possible to drop it after 3.4, in which case we should still update it now. Or we drop it before, or not at all.
Thoughts?