Improve Delegate to Coding Agent button workflow

[rebornix]

Currently, the Delegate to Coding Agent (cloud button) uses a modal dialog, chat response, and integrated terminal to transfer local chat sessions to a remote one. We should explore rendering all confirmations and progress in the chat view.

[rebornix]

Two additional workflows we should improve:

• feature request: more flexibility with send to remote agent #267716
• Better integration with prompt file (enabling blue button and improve https://github.com/microsoft/vscode/pull/253160/files)

[joshspicer]

Made decent progress with the API changes