Allow `qt_add_qml_module` target import/dependencies to work on imported targets

Right now there is a hard exclusion in `qt6_query_qml_module` against imported targets

    get_target_property(is_imported ${target} IMPORTED)
    if(is_imported)
        message(FATAL_ERROR
            "Only targets built by the project can be used with this command, "
            "but target \"${target}\" is imported."
        )
    endif()

This is unfortunate because using targets directly would make configure time checks much easier. Probably nowadays the import target restriction can be dropped if the appropriate properties are exported. But there might need some design question around the dependency URI passed by the user vs the one exported by the target.