Responsive headers for the Widget Inspector

[FMorschel]

Might have some relation to #8243 but I don't believe this should be the case anyway.

The headers for the Widget Inspector are not responsive in the same way as the widget tree.

If I shrink down the left side (Widget tree view) the content shows ... at the end.

If I do even more shrinking I can get both headers to overlap (even the icons).

I believe the tabs should have a minimum width and possibly an arrow button or something that indicates the user can "close" it (if that is wanted - potentially for small screens).