message editor: Only allow types of content the agent can handle (#36616)

Uses the new
[`acp::PromptCapabilities`](https://github.com/zed-industries/agent-client-protocol/blob/a39b7f635d67528f0a4e05e086ab283b9fc5cb93/rust/agent.rs#L194-L215)
to disable non-file mentions and images for agents that don't support
them.

Release Notes:

- N/A
2813073d7bAgus Zubiaga committed on 8/20/2025, 7:04:10 PM· committed by GitHubparent74ce543
11 files changedLine totals unavailable