Titlebar buttons are not keyboard focusable

[ThinkAndWander]

Describe the bug Buttons in the titlebar of a widget, like X or the star icon or favorite (in the demo) are not focusable by keyboard and cannot easily be navigated.

To Reproduce Go to dockview demo, click a tab that has another to its right and press tab to see focus land on that tab. Now that you have visual confirmation where the keyboard focus is, press tab again to go to the right-aligned buttons and you'll notice it has no effect, pressing enter does nothing, etc.

Repro's on Windows 11 Home running Firefox 143.0.1 64-bit