Add mouse tracking

[noelwelsh]

The terminal can somehow return mouse events. The best reference I've found is https://www.invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-Mouse-Tracking which is not as clear as I would like.

We should support this, though I'm not sure how it will fit into the design as I assume mouse tracking would send events continuously.

[gfinchMD]

JLine has support for MouseEvent. Could also use Lanterna if we need a bit more functionality.

How would you envisage the flow for this? Would the user enter some key that would begin returning mouse tracking events? Would we need some key to stop tracking mouse events?

I wonder if we could use a Stream here...

[noelwelsh]

I think the first abstraction that should be implemented is simply low-level enabling and disabling of mouse events, and parsing of mouse events when the terminal sends them. Here's Textual's parser for XTerm mouse codes and here is CrossTerm's representation of mouse events. If the user wants mouse events they would enable them (this should work similarly to modes like raw mode and application mode) and then events they read can include mouse events. The user decides when to read events and has complete control.

This is keeping with the philosophy of exposing the lower-level features (but wrapped up in a safer functional interface) and then building abstractions on top of these. I think any serious use would soon want some abstractions built on top of this (just like rendering would really benefit from a layout engine) but that's a different issue.