Fixes #5516

This is not a perfect solution, but an incremental improvement over what's there now.

• Prevents wrapping of status bar content
• If there is not horizontal space for the right-hand sidebar buttons, they collapse to a single button. That button shows a menu for selecting the tabs.

It doesn't solve the issues entirely, but does at least behave better.

Remaining issues:

• if the screen is even narrower, the collapsed button is pushed off screen
• only the RH tab buttons collapse

To get everything to behave on a very small screen will need a broader review. This PR isn't intended to solve everything.