Prefer better version matches

[gtristan]

This fixes the issue of parsing typically formulated release tarball URLs.

Consider the URL https://flying-ponies.com/releases/1.2/pony-flight-1.2.3.tgz.

Without this change, we only get the version 1.2 (the directory where we put all of the 1.2 releases).

After this change, we get 1.2.3.

This is achieved by explicitly supporting optional groups in the regex (which we already did, but in an not very specified way), and preferring more qualified matches by preferring matches which had more groups present in the match while iterating over all non-overlapping matches.

By causing the user to explicitly specify groups in the regex, we avoid the pitfall of relying on silly things like string length (where both strings "1.200" and "1.2.3" would be considered equally qualified).

[gtristan]

FWIW with the increased complexity, and increased clarity on how the regex string works - I would be more happy now to make a well defined utils function to do the guess work and share that code with the plugin repos.

[abderrahim]

This works fine, but I still think it's a bit too complicated.

I feel that extracting the basename from the URL and using just that for guessing the version is good enough. I went through all the buildstream projects I work on and couldn't find any instance where the version isn't in the basename.

That said, I won't block this.

[gtristan]

FWIW with the increased complexity, and increased clarity on how the regex string works - I would be more happy now to make a well defined utils function to do the guess work and share that code with the plugin repos.

I have now:

• Understood the regular expression nature a bit better
  • While it is possible to match repeating groups with a '*' wildcard, it is impossible to capture an arbitrary number of groups
• I have now created utils.guess_version() which reduces the implementer load by:
  • Doing the match iteration and preferring the match with the greatest amount of captured groups
  • Providing a central location to define the API contract for specifying version-guess-pattern