Backport upstream patch to fix graphics tablet hover events.

See the patch descriptions, this is a rather nasty bug preventing tooltips and other "mouse-over" events from working for all Qt applications that have no special graphics tablet support.

I believe this should also be pushed to buster-updates or similar due to the nature of the bug and the simple fix. I have done some preparation for this in https://salsa.debian.org/vermeeren-guest/qtbase/commits/buster, but there is no buster branch here at the moment for creating a MR.

Did not find a relevant Debian bug in BTS, I do have the issue myself however.