Agent: Use updated agent protocols

[abeatrix]

Update to use the latest changes for the agent protocols from sourcegraph/cody#5211

This let agent knows when we have a workspace added or removed.

Also updated to use View = WebviewView.Single, for webview to always run chats in sidebar view

22:05:32.767: [ProcessId:38884] [ThreadId:5] Debug [AgentJsonMessageFormatter.OnSerializationComplete] Sending to agent: {"jsonrpc":"2.0","id":3,"method":"workspaceFolder/didChange","params":[{"uris":["file:///C:/Users/BeatrixW/source/repos/TestingApp"]}]}