QML: Only release types if they aren't referenced anymore

QML: Only release types if they aren't referenced anymore

Just checking for references on m_compiledData is not enough. The
actual component can also be referenced. Thus it won't be deleted
on release(), but cannot be found in the type cache anymore.

Task-number: QTBUG-53761
Change-Id: I8567af8e75a078598e4fed31e4717134e1332278
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
(cherry picked from commit 2ac19881f92c94f4e9427bd9ff513210675f259e)

Gbp-Pq: Name qml_only_release_types_if_they_arent_referenced_anymore.patch