Chat: Support contributable chat context resources

[joaomoreno]

It would be fantastic if we could contribute chat context resources that could be attached in chat. For example, Pull Requests, here's a mock:

At a minimum the contribution should support:

• An icon
• A label
• A description (optional)
• Async resolution of the textual contents that are inserted into the prompt

For reference, see ResourceLabelFormatter and ResourceLabelFormatting.

cc Johannes Rieken (@jrieken) Ladislau Szomoru (@lszomoru)

[alexr00]

The proposal:

declare module 'vscode' {

	// https://github.com/microsoft/vscode/issues/271104 @alexr00

	export namespace workspace {

		export function registerChatContextProvider(selector: DocumentSelector, options: { providesList: boolean }, provider: ChatContextProvider): Disposable;

	}

	// Can't call it ChatContext because there's already a ChatContext in vscode.propsoed.chatSessionsProvider.d.ts
	export interface ProvidedChatContext {
		icon: IconPath;
		label: string;
		description?: string;
	}

	export interface ResolvedChatContext extends ProvidedChatContext {
		context: string;
	}

	export interface ChatContextProvider {

		provideChatContext(options: { resource?: Uri }, token: CancellationToken): ProviderResult<ProvidedChatContext[] | undefined>;

		resolveChatContext(context: ProvidedChatContext, token: CancellationToken): ProviderResult<ResolvedChatContext | undefined>;

	}

}