agent: Disable thinking when using inline assistant/edit file tool (#34141)

This introduces a new field `thinking_allowed` on `LanguageModelRequest`
which lets us control whether thinking should be enabled if the model
supports it.
We permit thinking in the Inline Assistant, Edit File tool and the Git
Commit message generator, this should make generation faster when using
a thinking model, e.g. `claude-sonnet-4-thinking`

Release Notes:

- N/A

crates/language_model/src/request.rs

@@ -391,6 +391,7 @@ pub struct LanguageModelRequest {
     pub tool_choice: Option<LanguageModelToolChoice>,
     pub stop: Vec<String>,
     pub temperature: Option<f32>,
+    pub thinking_allowed: bool,
 }
 
 #[derive(Serialize, Deserialize, Debug, Eq, PartialEq)]