Just like some of glib tools, wayland-scanner can be defined in the
pkgconfig dependency variables. Share code between gnome and wayland
modules into ModuleState.
This moves generally useful logic from GNOME module's
_get_native_binary() into find_program() implementation. We could decide
later to expose it as public API.
- Change `scope` kwarg to `public` boolean default to false.
- Change `side` kwarg to `client` and `server` booleans.
- Document returned values
- Aggregate in a single unit test because have lots of small tests
increases CI time.
Fixes: #10040.
Dylan Baker