edit prediction: Context debug view (#38435)

Adds a `dev: open edit prediction context` action that opens a new
workspace pane that displays the excerpts and snippets that would be
included in the edit prediction request.

Release Notes:

- N/A

---------

Co-authored-by: Bennet <bennet@zed.dev>

crates/edit_prediction_context/src/reference.rs

@@ -89,7 +89,8 @@ pub fn identifiers_in_range(
                     }
 
                     let identifier_text =
-                        &range_text[node_range.start - range.start..node_range.end - range.start];
+                        // TODO we changed this to saturating_sub for now, but we should fix the actually issue
+                        &range_text[node_range.start.saturating_sub(range.start)..node_range.end.saturating_sub(range.start)];
                     references.push(Reference {
                         identifier: Identifier {
                             name: identifier_text.into(),