Add native wayland plugin
Currently this plugin exists in plasma code due to a dependency on KWayland. This renders kidletime unusable outside of plasma even if the implementation is used.
This patch provides support directly in kidletime using QtWayland instead of relying on interim wrappers in KWayland that we hope to drop in KF6.
Migration is handled implicitly. If the plasma plugin is available either will be chosen at random. Then we will drop the plugin shipped by plasma next release.