fix QML property cache leaks of delegate items

fix QML property cache leaks of delegate items

Origin: upstream, https://code.qt.io/cgit/qt/qtdeclarative.git/commit/?id=b2862e2bd84d651c
Last-Update: 2021-01-26

The delegate items are destroyed through an event loop by a call to a
deleteLater(). This, however, doesn't work when the application is
in the process of exiting and the event loop is already closed (i.e.
we're in a stack unwinding part that starts after app.exec()).

Combat this situation by setting a parent of the to-be-deleted object
to some QObject that will be destroyed e.g. QCoreApplication::instance()
before the program finishes. As QObjects clean their children on
destruction, this will make sure that we cleanup the previously leaking
thing regardless of the event loop.

Gbp-Pq: Name fix_qml_property_cache_leaks.patch