KWin has supported the shared and formalised zxdg_decoration since
Plasma 5.16 which came out mid 2019.
Whilst it made sense to support them both for a while, it should not be
needed for future SDL releases.
We support both the org.freedesktop.ScreenSaver D-Bus API (same as the X11
backend) and the Wayland idle_inhibit_unstable_v1 protocol.
Some Wayland compositors only support one or the other, so we need both to
for broad compatibility.
Use zwp_keyboard_shortcuts_inhibit_manager_v1 to allow SDL applications
to capture system keyboard shortcuts like Alt+Tab when keyboard grab is
enabled via SDL_HINT_GRAB_KEYBOARD.
Now you don't need the latest Wayland installed to build with
newer protocols supported, as they'll build correctly; even if
your system can't use them, we can make intelligent decisions
at runtime about what's available on the current machine anyhow.
This also simplifies some logic and possible failure cases in
the configure and CMake scripts.
Fixes Bugzilla #4207.
