Prevent pane grid title bar content and controls from overlapping

[mtkennerly]

This fixes the content/controls becoming unreadable when they overlap in narrow panes.

Should this be configurable? For example:

enum Overlap {
    Allow, // existing behavior
    HideContent, // proposed behavior
    HideControls,
}

Before

before.mp4

After

after.mp4

[hecrj]

Looks great! It's definitely better than displaying overlapping elements.

Maybe we could make it configurable in a different PR? Your idea seems great.

Thank you 🙇