* Mir starts up and is able to display system settings
* x86_64 only for now, because at least ubuntu-app-test did not build
on aarch64
Based on PureTryOut's work. Getting it to this stage was a huge effort
(as it shows in the package count: 111(!)). See the merge request for
details.
[skip ci]: this won't finish in CI; ollieparanoid made sure that
everything builds for x86_64.
