#7108 GUI: When shift is pressed, tooltips disappear quickly without moving the mouse

[Ori Avtalion]

If I press "shift" to turn "Add Game" into "Mass Add", then hover over the button to see what it does, the tooltip will appear, then disappear very quickly, even though I didn't move the mouse.

If the shift key is pressed before the tooltip appears, the tooltip should only disappear when shift is released.

[Thierry Crozat]

Note that there were two attemps to fix this issue:
https://github.com/scummvm/scummvm/pull/716 (that doesn't work properly)
https://github.com/scummvm/scummvm/pull/730 (that works but is a bit heavy-handed for a temporary fix, modifying a lot of classes).

After some discussion with sev we think we should do some more foundamental changes in the way tooltips are handled in order to fix this and other issues.