Use quick pick separator objects instead of a kind

[TylerLeonhardt]

@connor4312 pointed out that the kind proposal for quickpick separators isn’t ideal because it would not be possible to have a single blank line separating two groups.

and @Tyriar pointed out that kind is ambiguous if you have a situation like this:

kind: ‘a’
kind: ‘b’
kind: ‘a’

we discussed this in the API sync as ‘doc-able’ but I do share the same feeling as he.

As such this implements:

	export interface QuickPickSeparator {
		type: 'separator';
		label?: string;
	}

	export interface QuickPickItem {
		type?: 'item';
	}

This is technically a compile-time break because .items on QuickPick needed to be updated.

Does this PR need to update vscode.d.ts? Is it possible for me to do this totally in vscode.proposed.d.ts?

cc @jrieken

[jrieken]

@connor4312 pointed out that the kind proposal for quickpick separators isn’t ideal because it would not be possible to have a single blank line separating two groups.

Are you sure about that? Can't I have some items without kind-property followed by another sequence of items with kind-property? Like [{label: a}, {label: b}, {label: c, kind: k}, {label: d, kind: k}]

and @Tyriar pointed out that kind is ambiguous if you have a situation like this:

I wouldn't say it's ambiguous but at most a programmer error (maybe even wanted). Isn't it the exact same as the following below? I wouldn't say any of the two is better or worse.

[
  { type: 'separator', label: a }, 
  { type: 'item', ... }, 
  { type: 'separator', label: b }, 
  { type: 'item', ... }, 
  { type: 'separator', label: a },
  { type: 'item', ... }
]

This is technically a compile-time break because .items on QuickPick needed to be updated.

Yes, this compile time breakage and also we haven't used type-discriminating properties anywhere. That would be a new concept for the API, which is something we generally try to avoid.

[TylerLeonhardt]

Are you sure about that? Can't I have some items without kind-property followed by another sequence of items with kind-property? Like [{label: a}, {label: b}, {label: c, kind: k}, {label: d, kind: k}]

Yes you can do that but that's not the scenario Connor is calling out. He's calling out:

Asdf
Asdf   
--------------------
Asdf
Asdf

Notice there is no label for this separator. There are no labels for each group. How would that work?

[TylerLeonhardt]

In your example k would be undefined... But then it would be treated as a part of the 1st group which is the problem.