libweston: add required_capabilities test suite quirk

This allows tests to skip when required capabilities are not present.
The output damage test for the shadow buffer case needs this.

required_capabilities is added to struct weston_testsuite_quirks which
is libweston public API just because there is no better place currently.
This is a little weird because the code to check it is in compositor,
not libweston.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

include/libweston/libweston.h

@@ -198,6 +198,8 @@ struct weston_testsuite_quirks {
 	bool gl_force_full_upload;
 	/** Ensure GL shadow fb is used, and always repaint it fully. */
 	bool gl_force_full_redraw_of_shadow_fb;
+	/** Required enum weston_capability bit mask, otherwise skip run. */
+	uint32_t required_capabilities;
 };
 
 /** Weston test suite data that is given to compositor