edit prediction: Try to expand context to parent treesitter region (#24186)

Also send the `speculated_output` (which is just the editable region) to
the llm backend

Closes #ISSUE

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>

crates/rpc/src/llm.rs

@@ -39,6 +39,7 @@ pub struct PredictEditsParams {
     pub outline: Option<String>,
     pub input_events: String,
     pub input_excerpt: String,
+    pub speculated_output: String,
     /// Whether the user provided consent for sampling this interaction.
     #[serde(default)]
     pub data_collection_permission: bool,