When a Tab subview exceeds the Tab Viewport, rendering of the tab border is clipped

[tig]

I did notice one unexpected behavior where the Title is not visible and becomes un-clickable when the Side is set to Right or Bottom:

I can repro this. Happens whenever a subview of the tab exceeds the viewport. Eg.

Originally posted by @tig in #4829 (comment)

[tig]

This only impacts Right and Bottom and can be addressed by enabling scrolling w/in the View that's the tab, which is the right thing to do.