qt_add_qml_module: TARGET dependency causes build failure

In the attached project, we run into a configure failure because (I assume) we try to defer running qmltyperegistrar to run at the project root level, but there we don't have access to the tool target.

Adding a find_package call in the top CML.txt fixes it, but might not always be feasible in larger projects.

The original project was provided by grecko