In commit 2c2291bbe0 (ENH: add new feature to ctest so that it can
cmake, build and run a test executable, 2004-01-07, v2.4.0~3483) ctest
was taught to recognize tests that run ctest itself and run them
internally instead of spawning a new process. This optimization was
removed by commit b9daa192af (ENH: Refactored CTest test execution code
into an object, 2009-08-19, v2.8.0~276) `cmCTestRunTest` replaced
`cmCTestTestHandler::ProcessOneTest`, which was eventually removed by
commit 5a5cc52230 (Fixed conversion warning on 64 bit machines,
2009-08-31, v2.8.0~241). Since then the optimization was only left in
`--build-and-test` mode, likely by accident, where it makes little
difference. Remove it to simplify the code.
Also drop the `--force-new-ctest-process` option, originally added by
commit 9255e40d81 (ENH: Add a way to force ctest to be a new process,
2004-05-10, v2.4.0~3101), since it no longer does anything.
The minimum CMake version for Qt6 is 3.16, so all the calls to
cmake_minimum_required() are updated here to enforce that
minimum. This will avoid any CMake version-related warnings
from Qt.
Avoid hard-coding Qt5 where the tests could now be using
Qt5 or Qt6.
Fixes: #22188
