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.toml

@@ -433,7 +433,7 @@ zlog_settings = { path = "crates/zlog_settings" }
 # External crates
 #
 
-agent-client-protocol = { version = "0.2.0-alpha.6", features = ["unstable"]}
+agent-client-protocol = { version = "0.2.0-alpha.8", features = ["unstable"] }
 aho-corasick = "1.1"
 alacritty_terminal = { git = "https://github.com/zed-industries/alacritty.git", branch = "add-hush-login-flag" }
 any_vec = "0.14"