agent2: Add now, grep, and web search tools (#35974)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Antonio Scandurra <me@as-cii.com>

Cargo.lock

@@ -191,6 +191,7 @@ dependencies = [
  "anyhow",
  "assistant_tool",
  "assistant_tools",
+ "chrono",
  "client",
  "clock",
  "cloud_llm_client",
@@ -227,10 +228,13 @@ dependencies = [
  "tempfile",
  "terminal",
  "theme",
+ "tree-sitter-rust",
  "ui",
+ "unindent",
  "util",
  "uuid",
  "watch",
+ "web_search",
  "which 6.0.3",
  "workspace-hack",
  "worktree",