assistant2: Decouple scripting tool from the Tool trait (#26382)

This PR decouples the scripting tool from the `Tool` trait while still
allowing it to be used as a tool from the model's perspective.

This will allow us to evolve the scripting tool as more of a first-class
citizen while still retaining the ability to have the model call it as a
regular tool.

Release Notes:

- N/A

Cargo.toml

@@ -8,7 +8,6 @@ members = [
     "crates/assistant",
     "crates/assistant2",
     "crates/assistant_context_editor",
-    "crates/scripting_tool",
     "crates/assistant_settings",
     "crates/assistant_slash_command",
     "crates/assistant_slash_commands",
@@ -119,6 +118,7 @@ members = [
     "crates/rope",
     "crates/rpc",
     "crates/schema_generator",
+    "crates/scripting_tool",
     "crates/search",
     "crates/semantic_index",
     "crates/semantic_version",