Sort extensions list alphabetically

[nihaals]

This was mentioned in #8955 (comment) but part of a more broad discussion.

It would be great if the extensions list (clicking the jigsaw icon in the toolbar by default) could be sorted alphabetically instead of only manual sorting. Finding the extension you want can be difficult otherwise when you have many extensions installed.

This same problem would also be eased with #6676 and #9398 but I think this would still be helpful as I don't want to even be able to sort them myself and have them auto-sorted.