Flyout menu: Render menu bottom-up if it exceeds the viewport height

[sukhwinder33445]

fixes #4594

[flourish86]

Basically it works.

I found a problem, though, which can best be seen on this screenshot:
in extreme conditions this could fire back and now exceed the top

Since the items outside of the screen aren't accessible anymore in this case, this should be prevented by restricting the height and make the flyout scrollable.

I made a quick mockup for this.

While the screenshot shows the collapsed version, this problem also occurs in the expanded version of the sidebar.

Another thing, that I discovered, was that the padding doesn't adapt (properly), when switching to the collapsed state. This way the last item in the scrollable part is covered by the fixed part of the menu. This is probably a different topic.

[sukhwinder33445]

Hi @flourish86,

I have discussed the problem of overflow with Johannes. It shouldn't happen in a normal screen size, and it's a different issue anyway. So for this PR we will leave it as it is.

not relevant