Core: add --no-window-frame command line option

Add a command line option to load Blender without a window frame.

Currently this is only used on Wayland, enabled for WITH_UI_TESTS since
attempting to load LIBDECOR caused the tests to crash on start on Fedora.
For tests there is no need to use LIBDECOR, so disable the window frame.
This can also be used by users who don't want to use the X11 fallback if
LIBDECOR can't be found.

Ref !147716

tests/python/CMakeLists.txt

@@ -121,6 +121,10 @@ if(WITH_UI_TESTS)
       # while this could be investigated, use windowed mode instead.
       # Use a window size that balances software GPU rendering with enough room to use the UI.
       --factory-startup
+      # Used so GHOST/Wayland doesn't attempt to load LIBDECOR
+      # which can fail on some systems, causing tests to fail.
+      # On other systems this is harmless.
+      --no-window-frame
       -p 0 0 800 600
       "${EXE_PARAMS}"
       "${ARGN}"