Use versioned UnicodeData.txt URL

[MichaelHatherly]

Should fix problems discussed in #18588 (comment). @tkelman is there anything I need to do to have juliacache mirror this, or does that happen automatically?

[tkelman]

either use deps/tools/jldownload instead of the download function, or prepend juliacache to the url

[tkelman]

If we're going to cache it here, we should probably change https://github.com/JuliaLang/utf8proc/blob/15e1819cdd326639a49481eb105dee242de99104/data/Makefile#L41 to avoid caching it in utf8proc, otherwise we might get the wrong unicode version cached if the two repos ever don't match.

[tkelman]

We could also maybe think about adding doc/deps to the travis caching, might save a minute or so of cloning metadata on every build? Though we'd have to invalidate the cache if we ever change the unicode version. Could checksum it perhaps, delete and retry on a checksum mismatch?

edit: on second thought this might leave a mess of every PR that updates metadata causing travis to re-upload a cache for the PR that differs from master, which we'd have to clear out manually every so often

[MichaelHatherly]

to avoid caching it in utf8proc, otherwise we might get the wrong unicode version cached if the two repos ever don't match.

Would the versions ever not match?

[tkelman]

Yes, if we make the change in one place then it won't match until we change it in the other. Even if we change it in both places at the exact same time, you'd need to do so on every branch, and never re-run a commit from before doing that.

[MichaelHatherly]

Ok, that makes sense, thanks. So we just need to not cache this file in utf8proc by removing the prefixed URLCACHE on that line, should that be done prior to merging this PR?

[tkelman]

Could be done after. But we should probably checksum the file here with jlchecksum to be sure we're getting the expected content

[MichaelHatherly]

(Hopefully I've done that jlchecksum correctly, seems to work alright I think...)

[stevengj]

Probably utf8proc should export some API to indicate what Unicode version it supports (JuliaStrings/utf8proc#91)