qt_add_qml_module should warn user about the use of unacceptable output qml directory

When configuring user project that use QML, the configuration doesn't warn users regarding name conflicts. qt_add_qml_module function should check if the target name conflicts with the QML OUTPUT_DIRECTORY name and suggest to either change the OUTPUT_DIRECTORY value, or/and make decision implicitly by adding qml prefix/suffix to output directory. Otherwise if URL matches the target name in qt_add_qml_module call this will lead to build errors like:

/usr/lib/gcc/x86_64-pc-linux-gnu/11/../../../../x86_64-pc-linux-gnu/bin/ld: cannot open output file <target>: Is a directory