Separate screen locker

[romangg]

The screen locker is only relevant on Wayland and only with KDE setup. This is a breaking change, as consumers need to update their setup code for the server.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 64.42308% with 37 lines in your changes are missing coverage. Please review.

Project coverage is 50.37%. Comparing base (ac77050) to head (27d0577).

Files	Patch %	Lines
como/desktop/kde/screen_locker.h	50.00%	10 Missing and 3 partials :warning:
como/base/wayland/server_helpers.h	62.50%	2 Missing and 1 partial :warning:
como/win/wayland/screen_lock.h	75.00%	2 Missing and 1 partial :warning:
tests/integration/lib/helpers.cpp	0.00%	3 Missing :warning:
como/desktop/kde/screen_locker.cpp	84.61%	1 Missing and 1 partial :warning:
como/input/wayland/cursor_image.h	0.00%	0 Missing and 2 partials :warning:
como/render/gl/scene.h	0.00%	2 Missing :warning:
como/win/wayland/window.h	33.33%	1 Missing and 1 partial :warning:
tests/plasma/main_wayland.cpp	0.00%	2 Missing :warning:
como/input/wayland/keyboard_redirect.h	0.00%	0 Missing and 1 partial :warning:
... and 4 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #21 +/- ## ========================================== - Coverage 51.02% 50.37% -0.66% ========================================== Files 938 941 +3 Lines 87395 87404 +9 Branches 45013 45460 +447 ========================================== - Hits 44593 44026 -567 - Misses 38238 39427 +1189 + Partials 4564 3951 -613 ```

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