Clean up Branches: Rename to match d.o pattern & remove merged ones.

Now that we have GitLab it is really easy to view and manage branches.

Last night I went through most of the hosting branches at https://git.drupalcode.org/project/hosting/-/branches and:

1. Delete merged branches.
2. Manually check issues of branches to see if they have been marked as closed.
3. Ensure there are no lingering unmerged commits.
4. Rename branches to match the drupal.org pattern ISSUENUMBER-DESCRIPTION
5. Update useful branches with latest commits from primary branch, resolving conflicts where necessary.