Introduce LanguageModelToolUse::raw_input (#29322)

This is to enable alternative streaming solutions at the application
layer. I'm not sure we really should have performed parsing of the input
at this layer. Either way I want to experiment with streaming approaches
in a separate crate on a branch, and this will help.

/cc @maxdeviant @bennetbo @rtfeldman

Closes #ISSUE

Release Notes:

- N/A

crates/language_model/src/language_model.rs

@@ -186,6 +186,7 @@ where
 pub struct LanguageModelToolUse {
     pub id: LanguageModelToolUseId,
     pub name: Arc<str>,
+    pub raw_input: String,
     pub input: serde_json::Value,
     pub is_input_complete: bool,
 }