This change removes all traces of wl-shell in the test suite. That's a
prerequisite for dropping wl-shell support in KWin.

Given that wl-shell and xdg-shell are not interchangeable, some tests
were removed and initialization sequence in some tests was adjusted.

The most notable change is ensuring that each plasmashell window sets
its role and initial position before committing the surface. Setting
those properties before the first surface commit is important because
our window placement code needs to know window type in order to
avoid maximizing panels, popups, etc.