Port the RuleSettings and KCM to store and use a list of virtual desktop
UUIDs, instead of the previous x11 positional id, continuing the work on
This allows to set a rule with several desktops on Wayland.
On X11 it has no visible change for the user, but internally it uses the
more modern concept, helping to simplify the related code.
The relevant key on kwinrulesrc changes from `desktop` to `desktops`.
A kconf_update script handles the migration.
Once in a while, we receive complaints from other fellow KDE developers
about the file organization of kwin. This change addresses some of those
complaints by moving all of source code in a separate directory, src/,
thus making the project structure more traditional. Things such as tests
are kept in their own toplevel directories.
This change may wreak havoc on merge requests that add new files to kwin,
but if a patch modifies an already existing file, git should be smart
enough to figure out that the file has been relocated.
We may potentially split the src/ directory further to make navigating
the source code easier, but hopefully this is good enough already.
