Make the assistant panel initially active for the right dock

[cole-miller]

This means that workspace::ToggleRightDock will open the assistant if no right-dock panel has been manually activated, instead of the chat as before. Also cleans up the active_panel_index logic a bit.

cc @nathansobo

Release Notes:

• Make workspace::ToggleRightDock open the assistant panel if no right-dock panel has yet been activated

[SomeoneToIgnore]

A minor note: we have a way to disable assistant with

zed/assets/settings/default.json

Lines 520 to 521 in 515e31a

	// Whether the assistant is enabled.
	"enabled": true,

and implicitly with

zed/assets/settings/default.json

Line 498 in 515e31a

"button": true,

people with either of these disabled won't be very pleased with the change, it seems.

Frankly, I am not fold of this too as I prefer the terminal to be there instead, but it's not important.

[cole-miller]

@SomeoneToIgnore thanks! I'll look into making this degrade gracefully when the assistant is disabled in settings.

Frankly, I am not fold of this too as I prefer the terminal to be there instead, but it's not important.

I didn't think of this because I always have the terminal open in the bottom dock, not the right. I don't think this should break a workflow where you manually make a terminal active for the right dock and toggle it with the action; and my impression from testing was that in the status quo the chat panel occupies that active slot at startup. Am I missing something?

[SomeoneToIgnore]

It's another edge case (not important, as stated), where I have

"terminal": {
  "dock": "right"
},

in the settings and clear the DB, making the next startup "default".

[cole-miller]

I think the current approach is too heavy-handed; thinking about alternatives.