Update update status XML for Drupal 9 and contrib semantic versioning

Yes, the existing system will be in place indefinitely. It may end up being okay to keep extending.

Ryan had an idea in a meeting this came up in a meeting.

Right now we have API-compatibility-specific histories like

• https://updates.drupal.org/release-history/token/7.x
• https://updates.drupal.org/release-history/token/8.x

And all for everything:

• https://updates.drupal.org/release-history/token/all

We could add current which:

• Is generally the same XML format.
• Has releases with 8.x or 9.x compatibility, plus releases without API compatibility. Contrib releases made in the future with semver will not have the API compatibility part of their version number #2681459: Support contrib semver releases
• Removes any tags that core doesn’t use and aren’t otherwise useful.
• Adds any newly-necessary data, like support for #2991207: Drupal core should inform the user of the security coverage for the site's installed minor version including final 8.x LTS releases

Since #3085041: Drupal core 9.x.x releases should not attach API compatibility term, Drupal 9.0.x is not at https://updates.drupal.org/release-history/drupal/9.x. That just has some junk about the former “9.x” release which I’ll remove, see #2864048: Delete the 9.x branch and its associated release.

Also with 8.x-… modules optionally being compatible with Drupal 9, grouping modern/current releases by 8.x or 9.x doesn’t make sense.

Probably not the whole scope. XML isn’t a “cool” file format, but this really should be backported to D8, #3074993: Use "current" in update URLs instead of CORE_COMPATIBILITY to retrieve all future updates. Completely changing the format would probably kill any chance of that happening.

(I could see putting semver contrib releases in the 8.x XML if their .info file says they are compatible with D8. That would probably confuse some logic in update.module on sites that haven’t updated.)

This should not affect existing update status XML, it adds a new …-current.xml, which is described at #3074993-18: Use "current" in update URLs instead of CORE_COMPATIBILITY to retrieve all future updates