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

crates/zed/Cargo.toml

@@ -98,7 +98,6 @@ remote.workspace = true
 repl.workspace = true
 reqwest_client.workspace = true
 rope.workspace = true
-scripting_tool.workspace = true
 search.workspace = true
 serde.workspace = true
 serde_json.workspace = true