Release graphics resources for every extension type

The resource cleanup only matched Type::RenderExtension exactly, so
extensions carrying any other extension type fell through to plain
deletion. The check predates the TextureProvider type;
QSSGRenderTextureProviderExtension sets HasGraphicsResources and
therefore reaches the cleanup, but its registered render result was
never released. The same applies to user-defined extension types,
which combine the User and Extension base types.

Pick-to: 6.12 6.11 6.8
Task-number: QTBUG-149579
Change-Id: I7f544d21caef2dde0a22fb37ed16a31ebc05a5d3
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>