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
On Windows, imported shared libraries which only have an
`IMPORTED_IMPLIB` set fail if they are depended upon by a target using
automoc. Add a test for the behavior of depending upon all imported
target types from an automoc-using target.
