wayland: Implement 'DISABLED' cursor mode

This implements support for the 'DISABLED' cursor mode, which
effectively means locking the pointer to the surface. The cursor is also
explicitly hidden.

This adds two new build dependencies: wayland-scanner and
wayland-protocols.

Closes #708.

CMake/modules/FindWaylandProtocols.cmake

@@ -0,0 +1,26 @@
+find_package(PkgConfig)
+
+pkg_check_modules(WaylandProtocols QUIET wayland-protocols>=${WaylandProtocols_FIND_VERSION})
+
+execute_process(COMMAND ${PKG_CONFIG_EXECUTABLE} --variable=pkgdatadir wayland-protocols
+                OUTPUT_VARIABLE WaylandProtocols_PKGDATADIR
+                RESULT_VARIABLE _pkgconfig_failed)
+if (_pkgconfig_failed)
+    message(FATAL_ERROR "Missing wayland-protocols pkgdatadir")
+endif()
+
+string(REGEX REPLACE "[\r\n]" "" WaylandProtocols_PKGDATADIR "${WaylandProtocols_PKGDATADIR}")
+
+find_package_handle_standard_args(WaylandProtocols
+    FOUND_VAR
+        WaylandProtocols_FOUND
+    REQUIRED_VARS
+        WaylandProtocols_PKGDATADIR
+    VERSION_VAR
+        WaylandProtocols_VERSION
+    HANDLE_COMPONENTS
+)
+
+set(WAYLAND_PROTOCOLS_FOUND ${WaylandProtocols_FOUND})
+set(WAYLAND_PROTOCOLS_PKGDATADIR ${WaylandProtocols_PKGDATADIR})
+set(WAYLAND_PROTOCOLS_VERSION ${WaylandProtocols_VERSION})