Long-standing repaint-flicker issue.

[tig]

There have been long-standing repaint-flicker issues in the libarary. At one point I hoped I fixed them all with a fix to how ClearWhenVisibleFalse was in play.

However, I did something in this #3323 that has caused the problem to re-appear. I've spent HOURs trying to track it down unsuccessfully.

Here I held down Ctrl-G to repro:

Originally posted by @tig in https://github.com/gui-cs/Terminal.Gui/issues/3323#issuecomment-2057152669

See the above thread for a bunch of discussion between @BDisp and I on possible causes... None seem to explain it.