[SuperEditor][Android][iOS] - Add tooling to more easily create keyboard toolbar experiences

[matthew-carroll]

Editing text on mobile typically requires a toolbar that sits on top of the keyboard. For more sophisticated editors, it's also common to switch between the software keyboard and a panel with buttons. The panel with buttons takes larger-scale actions on the document - things that don't always apply when editing, and things that might need more room than a little icon on the toolbar.

Let's evaluate what kind of tooling we could provide that makes it faster and easier for apps to setup mobile keyboard editing toolbars and panels.

@angelosilvestre let's begin with ~1hr of investigation into the value we can provide here, the way others are already doing this, how we can/should interact with the keyboard, etc. Then let's use the remaining time to work on the tools.