Typo

GIT_SILENT
Wayland and QtWayland protocol scanners

Add a couple of find modules for wayland-scanner and qtwaylandscanner.
These modules find the respective executables and create a target that
points to the executable.

Targets are respectively Wayland::Scanner and Wayland::QtScanner.

There are also macros to generate C protocols with wayland-scanner and
C++ wrappers with qtwaylandscanner.

REVIEW: 120034
If find_dependency() fails, so should the Config file it is in

REVIEW: 120655
Upgrade ECM version to 1.4.0.