Agent: support multi-root workspace on workspace change events

[abeatrix]

This PR addresses the issue where the workspace folder changes were not being handled correctly. The setWorkspaceFolders function has been updated to correctly add, remove, and update the workspace folders in the workspaceFolders array.

Additionally, the ChatsController has been updated to handle clients with a single webview, where the sidebar chat view is the only supported chat view.

Test plan

Green CI. Added test coverage for the workspace change in vs code shim.

Connect Agent to client to test the following:

• Test adding a new workspace folder
• Test removing a workspace folder
• Test removing the last workspace folder
• Test switching between workspace folders in a client with a single webview check the protocol trace logs to verify the events

Changelog

• Agent: Update workspace folder changes handling to support multi-root workspace
• Agent: Handle clients with a single webview