Improve claude tools (#36538)

- Return unified diff from `Edit` tool so model can see the final state
- Format on save if enabled
- Provide `Write` tool
- Disable `MultiEdit` tool
- Better prompting

Release Notes:

- N/A

crates/agent_servers/Cargo.toml

@@ -29,6 +29,7 @@ futures.workspace = true
 gpui.workspace = true
 indoc.workspace = true
 itertools.workspace = true
+language.workspace = true
 language_model.workspace = true
 language_models.workspace = true
 log.workspace = true