Pass model to tools (#244323)

* Pass model to tools
When tools make requests, they should use the right model. So we
- save the model id on the request
- look it up when the tool is invoked
- resolve it to a LanguageModelChat in the EH

* Fix build

src/vscode-dts/vscode.proposed.chatParticipantAdditions.d.ts

@@ -433,4 +433,8 @@ declare module 'vscode' {
 		Medium = 2,
 		Full = 3
 	}
+
+	export interface LanguageModelToolInvocationOptions<T> {
+		model?: LanguageModelChat;
+	}
 }