Install and test zlib, bzip2 in CI builds

[NWilson]

Also, ensure that the libreadline and libeditline builds pass (although we can't really test whether these work).

[carenas]

maybe use editline in the alpine job for variety?

not sure why this is needed though (maybe something to add to the commit message on the rationale), since the test should work regardless and it is mostly useful when the tool is used interactively

[carenas]

we also have libeditline support (which is preferred due to license in the BSD)

[NWilson]

OK, I can use that.

I really wanted the CI to be testing the zlib/bzip2 support; and when I added that, I thought it would be reasonable to throw in a test for readline too (although we're only testing it builds & links, and not really exercising the readline support).

The readline support is not really important, since it's just test-only. It would be OK if it broke. But the zlib support can't break.

[carenas]

truth is that pcre2grep was always treated as a more complicated version of pcre2demo, and that is the only tool that needs the dependency (the library does not)

agree though we are better off testing and treating it more like a product, as it seems people seem to think it is almost as useful as GNU grep of ripgrep (which funny enough also uses PCRE2)

[NWilson]

It would be nicer if other people could maintain the frontend (like even GNU grep has -P now for PCRE!)

But I guess if people are using pcre2grep, then it needs to be tested.

I'm happy with this PR. We only need a minimal effort (smoke test) to exercise these external library integrations.

[zherczeg]

LGTM