Explore grouping options for toolbox panels

[zepumph]

From #166 and very related to phetsims/sun#874 and phetsims/scenery-phet#844.

An alt input toolbox pattern was established back in #166 (comment), but a nice improvement would be to have all items in the toolbox be a single item in focus order. We won't work on this now, but we should work closely with the above issues in case there is a common code module that could achieve this for many different interactions.

Interaction:

1. Tab to the whole toolbox (with multiple items inside)
2. Use arrows to cycle through the tool icon you want
3. Button interaction to "grab" or "create" that tool.
4. Focus transfers to the created tool, and you can drag it around with normal keyboard dragging interaction.