Amends c204b2205c045c2e7dbab442cca2b9f17f5cc9ae Consider what happens when rapidly creating and destroying MultiEffect { } instances: due to the reference counting, the corresponding QSGMaterialType* is moved to the graveyard (emptied typically only on explicit releaseResources() or when exiting), and never reused. However, that reuse is very much desired, because other components in the system, e.g. the scenegraph renderer, uses that type pointer value as keys in its caches. Ideally a ShaderEffect with the exact same shaders should give the same QSGMaterialType* value. Pick-to: 6.7 6.6 6.5 Fixes: QTBUG-124281 Change-Id: I01dabc8cc361036ccd735099d42ae321d267ab26 Reviewed-by: Christian Strømme <christian.stromme@qt.io>