Enable per-corner border radius in tooltip

[etimberg]

Resolves #9533

There are cases where this will look bad. For example:

[kurkle]

Looks good. Should the radius be limited to something doable?

[etimberg]

I can look into limiting it 0.5 * width/height

[kurkle]

I think it would be ideal to handle that in toTRBLCorners, so it would not need to be implemented everywhere. But I'm ok without limiting the values, until its needed for some use case.

[etimberg]

Sure, we can add the limit later