acp: Support session modes (e.g. CC plan mode) (#37632)

Adds support for [ACP session
modes](https://github.com/zed-industries/agent-client-protocol/pull/67)
enabling plan and other permission modes in CC:


https://github.com/user-attachments/assets/dea18d82-4da6-465e-983b-02b77c6dcf15


Release Notes:

- Claude Code: Add support for plan mode, and all other permission modes

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

Cargo.lock

@@ -196,9 +196,9 @@ dependencies = [
 
 [[package]]
 name = "agent-client-protocol"
-version = "0.2.0-alpha.6"
+version = "0.2.0-alpha.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d02292efd75080932b6466471d428c70e2ac06908ae24792fc7c36ecbaf67ca"
+checksum = "08539e8d6b2ccca6cd00afdd42211698f7677adef09108a09414c11f1f45fdaf"
 dependencies = [
  "anyhow",
  "async-broadcast",