enhance(main/zsh): Cherry-pick PCRE2 support for `zsh/pcre` module

[TomJo2000]

This PR adopts Arch Linux's cherry-picks from upstream Zsh to update the zsh/pcre module to use pcre2 instead of the now deprecated pcre^1.

This change is already present in the upstream project's master branch, and is slated for inclusion in the 5.10 release of Zsh. _{Which will presumably happen sometime prior to the heat death of the universe.}

This PR also contains:

• Switching the source URL for Zsh to the official Zsh FTP site.
• Creating a symlink for zsh-$version in place of the zsh-$version hardlink provided by other packagings of Zsh
• And some minor build script cleanup.

[TomJo2000]

Ah crap I just got around to testing this on-device and that didn't quite work it looks like.

Ah it's not applying the patch. But `termux_step_post_get_source` should happen before `termux_step_patch_package`... 

Oh... I downloaded it into the wrong directory.

[TomJo2000]

Tracked it down to needing to autoreconf -fi first. In addition to actually downloading the patch to the right location.

Scratch that. I don't know anymore at this point.

[TomJo2000]

The first configure run, for config.modules doesn't pick up -lpcre2-8, the second one for Zsh itself does. But since the module one doesn't, zsh/pcre doesn't get linked to pcre2.

I'm just gonna push my changes to this branch and worry about it tomorrow.

Edit: Apparently I should just hold my tongue because I just noticed I had commented out the `autoreconf -fi` to diff the logs. And after re-enabling it, it works as it should.  Works like a charm.

[TomJo2000]

Looks like it isn't removing the pcre patch from the package directory properly after patching, I didn't get the time to look into why today.