Comparing the layer contents to the backingstore surface doesn't make
sense when we're single buffered since we're always using the same
surface.
And once Core Animation has picked up on the surface it's not enough to
just keep drawing to it, we also need to tell Core Animation that the
contents has changed.
Change-Id: I517a0b7a3ba7e9d96033465c9bd5a192985643ac
Fixes: QTBUG-81071
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
0c6b4dd4ad