Use the term "edit prediction" over "inline completion" (#24211)

Note that this does *not* involve any breaking code changes.

cc @0xtimsb - I didn't change any settings or anything here. That can
happen separately!

Release Notes:

- N/A

crates/copilot/src/copilot_completion_provider.rs

@@ -393,7 +393,7 @@ mod tests {
             assert_eq!(editor.text(cx), "one.\ntwo\nthree\n");
         });
 
-        // Ensure existing inline completion is interpolated when inserting again.
+        // Ensure existing edit prediction is interpolated when inserting again.
         cx.simulate_keystroke("c");
         executor.run_until_parked();
         cx.update_editor(|editor, _, cx| {