Add ECMQueryQt module, which encompases both Qt5 Qmake and Qt6 qtpaths

Basically copied ECMQueryQmake to ECMQueryQt, added copyright based on git log, with the BSD 3-clause license; based on the contents of the README.rst file at the initial commit (commit 96e7fb99 by Rohan Garg) of ECMQueryQmake, the README file says: All code is licensed under the BSD 3-Clause license.

Will CC active devs in the MR and email Rohan Garg to confirm.

Then added qtpaths CMake code path, basically you can use query_qt with Qt5 (same syntax, so a drop-in replacement for query_qmake); and Qt6.

The plan is to deprecate ECMQueryQmake in favour of the new module (had to be done that way as the old module had "qmake" in the name and that could be a bit confusing).