Port assistant crate to Zed2 (#3513)

This PR contains the initial port of the `assistant` crate to Zed2.

Release Notes:

- N/A

Cargo.lock

@@ -376,6 +376,47 @@ dependencies = [
  "workspace",
 ]
 
+[[package]]
+name = "assistant2"
+version = "0.1.0"
+dependencies = [
+ "ai2",
+ "anyhow",
+ "chrono",
+ "client2",
+ "collections",
+ "ctor",
+ "editor2",
+ "env_logger 0.9.3",
+ "fs2",
+ "futures 0.3.28",
+ "gpui2",
+ "indoc",
+ "isahc",
+ "language2",
+ "log",
+ "menu2",
+ "multi_buffer2",
+ "ordered-float 2.10.0",
+ "parking_lot 0.11.2",
+ "project2",
+ "rand 0.8.5",
+ "regex",
+ "schemars",
+ "search2",
+ "semantic_index2",
+ "serde",
+ "serde_json",
+ "settings2",
+ "smol",
+ "theme2",
+ "tiktoken-rs",
+ "ui2",
+ "util",
+ "uuid 1.4.1",
+ "workspace2",
+]
+
 [[package]]
 name = "async-broadcast"
 version = "0.4.1"
@@ -11852,6 +11893,7 @@ dependencies = [
  "activity_indicator2",
  "ai2",
  "anyhow",
+ "assistant2",
  "async-compression",
  "async-recursion 0.3.2",
  "async-tar",
@@ -11911,6 +11953,7 @@ dependencies = [
  "rust-embed",
  "schemars",
  "search2",
+ "semantic_index2",
  "serde",
  "serde_derive",
  "serde_json",