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/scripting_tool/Cargo.toml

@@ -14,7 +14,6 @@ doctest = false
 
 [dependencies]
 anyhow.workspace = true
-assistant_tool.workspace = true
 collections.workspace = true
 futures.workspace = true
 gpui.workspace = true