Support and prefer QML_IMPORT_PATH over QML2_IMPORT_PATH

The 2 is meaningless.

Task-number: QTBUG-85064
Change-Id: I9f140155d274c691b5eab1285d9b7153f9f93a87
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>