Merge point for GTK 4 port

This tag is the final commit from the GTK 4 port which is incomplete,
but now merged onto main for nightly progress.

This tag allows us to look back at history without the expectation that
further development happens on the wip/gtk4-port branch.

Please continue to make progress with the merged state on main.

Thanks to everyone that contributed to the branch, and my appologies that
commit history could not be accurately maintained. The drift from main
was just too much to handle and so I had to make a best effort case to
break things up in to more useful/meaningful chunks as part of the merge

We were nearly 2000 commits off main, and that compressed down to about
250 commits.

Thanks again for all the hard work!