Changes pro2cmake to handle load(qt_app) projects and write out
qt_internal_add_app calls.
Also adds handling of macOS and Windows specific resource files for Qt
apps only.
Task-number: QTBUG-85757
Change-Id: I994d8d19ab2ae366a985cab7894b97d6a278a56f
Reviewed-by: Cristian Adam <cristian.adam@qt.io>