QML module files copied to build dir have nothing depending on them

qt6_target_qml_sources() defines calls to add_custom_command(OUTPUT) for each qml file or resource file given to it. But no target depends on those copied files, so there is nothing in the build rules to make those files get updated if the source files change. The files will therefore only get updated when CMake runs (there is an execute_process() call to also copy the files at configure time).