Reduce the amount of code required to add a qml plugin to cmake
by making add_qml_module wrap the add_qt_plugin code where required.
add_qml_module will also create a dummy target so that qml files
will appear as source files in an IDE when no cpp files are present.
CXX_MODULE qmake parameter has been dropped in favor of an
explicit IMPORT_VERSION parameter, since it was only used to
determine the version when the IMPORT_VERSION was not specified.
Change-Id: I4a4b626566720d04c62d246ca521db8c4a95b10f
Reviewed-by: Qt CMake Build Bot
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
31341ad63a