Needed for the upcoming static plugin mechanism, where we have to
extract the list of Qt module dependencies of a target and then extract
the plugins associated with those modules.
To do that we need to recursively collect the dependencies of a given
target.
Rename the moved functions to contain the __qt_internal prefix.
Also rename the existing QtPublicTargetsHelpers.cmake into
QtPlatformTargetHelpers.cmake to avoid confusion with the newly
introduced QtPublicTargetHelpers.cmake.
Task-number: QTBUG-92933
Change-Id: I48b5b6a8718a3424f59ca60f11fc9e97a809765d
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
