CMake: Add a RunCMake test for feature resolution

qt_feature() lets DISABLE win over ENABLE, which wins over
AUTODETECT and CONDITION, and forces a feature OFF when EMIT_IF does
not hold. None of that was tested; RunCMake/QtFeatureExclusiveGroup
only covers exclusive groups.

Port the assertions from cmake/tests/features, which has not been
runnable for a long time, including its check that feature values are
visible in subdirectories.

Change-Id: I9a4674b5e544f5e1bb919f6e96dc23a173aab0d6
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>