Fix SGR/UTF8 mouse reporting in terminal panes

[imsnif]

This is a fix for: #1633

Main changes:

1. We now track which mouse button was released when collecting user input (rather than sending a generic "release" event on to the zellij server).
2. DECSET/DECRST now loop through all arguments rather than just taking the first one (oops!)
3. Mouse mode is now tracked as "NoEncoding", "SGR" or "UTF8" rather than true/false
4. We now also track the mouse tracking method as "Off", "Normal" and "ButtonEventTracking", reporting nothing, button press + release and button press + release + hold respectively.
5. We send the relevant events from 4 with the relevant encoding from 3 to the terminal panes as needed. Defaulting to utf8 encoding.

There's room to implement AnyEvent tracking in supported terminals, but that's out of scope for this PR.

[imsnif]

@tlinford - if you could give this a spin to make sure I didn't break any mouse stuff that I'm not aware of that would be great :)

@AutumnMeowMeow - if you have the time and feel like it, would you like to check this change out and let me know what you think?

[AutumnMeowMeow]

@imsnif Testing inside vttest, I see the following issues:

• Off-by-one coordinates: SGR mode (1006), button-event (1002), during a drag-with-button-down: the coordinates are incorrectly +1 rows +1 cols. The button-down and button-up coordinates are correct.
• Off-by-one coordinates: UTF8 mode (1005), normal-event (1000), during a button-release: the coordinates are incorrectly +1 rows +1 cols. The button-down coordinates are correct.
• Off-by-one coordinates: UTF8 mode (1005), button-event (1002), during a button-release and during a drag-with-button-down: the coordinates are incorrectly +1 rows +1 cols. The button-down coordinates are correct.
• When a test is exited via 'q', mouse tracking is still on and not off. You are missing the corresponding cases from here for 1000, 1002, 1003 (TBD) that belong here.

[imsnif]

Thanks @AutumnMeowMeow ! I guess I was pretty tired when I submitted this. I even glanced over these in the tests :) All fixed.

[AutumnMeowMeow]

@imsnif It's better now, but I still see the following:

• Button 2 (usually middle button) is not reporting on button-down or button-down-and-drag, but is reporting on button-up/release.
• In SGR coordinates, when button 2 reports button-up, it incorrectly reports it as button 1 (code 0) button-up.
• In both UTF-8 and SGR coordinates, button-down-and-drag is not being reported as a drag (button code + 32), but rather as button-down (button code).

[imsnif]

@AutumnMeowMeow - all fixed. These were part misunderstanding on my part, and part Zellij not previously fully supporting middle-clicks. Thanks again!

[tlinford]

@imsnif gave it a test, all of these seem fine to me:

• pane/tab selection with mouse
• moving floating pane
• selecting text
• scrolling with mouse wheel
• interacting with nvim with set mouse=a

[AutumnMeowMeow]

I confirm normal-event and button-event are working correctly for me:

simplescreenrecorder-2022-08-16_13.46.27.mp4

Any-event is not yet working, so no tracking mouse cursor tracking, but that is expected. Click/drag/release and wheel-up/wheel-down are working well.

I would say #1633 is fixed with this. :)

[imsnif]

Fantastic! Thank you both for your help.