WIP tracking issue: Improved keyboard support

[martenbjork]

Navigation lists

• Ideally, lists should be navigatable with arrow up / down. I frequently find myself clicking an item in the Blueprints view and wanting to go to the next/prev item using the arrow keys.

• Ideally, you should be able to toggle children using arrow left/right. This conflicts with the timeline, which currently subscribes to arrow left/right commands.

How can this conflict be resolved?

Toggle panel focus order

The icons for toggling different panels receive focus in the wrong order when tabbing through the top bar.

Drop downs

• You should be able to go up and down in drop downs using the keyboard.
• You should be able to jump in drop downs by typing a character. The native (mac os) behavior is that typing a character will jump to the first drop down item that starts with that character. In a country picker for instance, typing s might highlight Sweden.

[abey79]

Related: emilk/egui#3272