Update widget mouseover when scrolling panels.

[pchote]

The new map editor remains blocked by #8017, so here's another chunk that can be reviewed in parallel.

This fixes a long-standing bug where scrolling a scrollpanel does not update the mouseover region beneath it. A simple repro/fix case is to mouse-over a game in the server browser, and then scroll the panel with the mousewheel. The highlighted game will now correctly change.

[Mailaender]

I solved this differently Mailaender@1f1fee0 in #4496.

[pchote]

Indeed, but that only solves about 1/4 of the problem: there are two places where the scrolling occurs, and that doesn't handle mouse entry for the newly moused over widget.

[obrakmann]

This works as promised, 👍

[Mailaender]

I can't see tooltips in the server browser and believe we never had some. However the faction tooltips seem to work better in the lobby when scrolling. ✅ I had some trouble with tooltips not appearing in the lobby maybe upon leave and restart, but I am not sure if this is introduced by this or maybe just a performance flaw.

[pchote]

@Mailaender: this isn't about tooltips, but hover / mouseovers in general.

[pchote]

Rebased to try and force a refresh of appveyor and nuget (feels more like crappveyor and noget lately :s).

[Mailaender]

Well. You did not change any .csproj files and nothing here is covered by unit tests so I am fine with Travis CI being green.

[Mailaender]

Scrolling indeed works much better for long lists. It now updates the high-lighted reason not just at the end of the scroll when moving the mouse again.

[Mailaender]

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