Explore a generic accessibility view

[Tyriar]

We currently have the terminal accessible buffer and there is the idea floating around that we may want to show some of the chat experience in a monaco editor as it's more friendly that switching screen reader modes.

Similar to #183363, what if there was a generic "accessible view" command that in general would take the focused element and put its textContent into a popup? Components could then register their own custom handlers, so the terminal for example would define how to get the terminal content out and other features of the terminal accessible buffer (like cmd/ctrl+up?).

This could also share the monaco editor for #183363 for better perf/memory usage.