As QPropertyAlias was public by accident in 6.0, we have to ensure that
it still works in 6.2.
This re-adds some tests for it, and reimplements the unlinking
functionality. To avoid performance regressions in hot-paths,
a new unlink_fast function is added, which behaves like the old unlink:
It ignores the special handling for QPropertyAlias, so that we can skip
the tag check. It is only used in QPropertyObserverNodeProtector and
clearDependencyObservers, where we already know the type of the
observer.
Fixes: QTBUG-95846
Pick-to: 6.2
Change-Id: Ifb405b8327c4d61c673b1a912ed6e169d27c2d8f
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
e4d62651c2