completions: Add subtle/eager behavior to Supermaven and Copilot (#35548)

This pull request introduces changes to improve the behavior and
consistency of multiple completion providers
(`CopilotCompletionProvider`, `SupermavenCompletionProvider`) and their
integration with UI elements like menus and inline completion buttons.
It now allows to see the prediction with the completion menu open whilst
pressing `opt` and also enables the subtle/eager setting that was
introduced with zeta.

Edit: I managed to get the preview working with correct icons!
<img width="909" height="232" alt="image"
src="https://github.com/user-attachments/assets/65800e67-4bc4-40f8-be78-806fcfe74ad9"
/>
<img width="1460" height="318" alt="CleanShot 2025-08-04 at 01 36 31@2x"
src="https://github.com/user-attachments/assets/15651405-720f-465f-a13c-c7470817810a"
/>

Correct icons are also displayed:
<img width="244" height="96" alt="image"
src="https://github.com/user-attachments/assets/0b8a687f-73e3-452d-aefb-784c52831b73"
/>


Edit2: I added some comments, would be very happy to receive feedback
(still learning rust)

Release Notes:

- Added Subtle and Eager edit prediction modes to Copilot and Supermaven

crates/edit_prediction/src/edit_prediction.rs

@@ -61,6 +61,10 @@ pub trait EditPredictionProvider: 'static + Sized {
     fn show_tab_accept_marker() -> bool {
         false
     }
+    fn supports_jump_to_edit() -> bool {
+        true
+    }
+
     fn data_collection_state(&self, _cx: &App) -> DataCollectionState {
         DataCollectionState::Unsupported
     }
@@ -116,6 +120,7 @@ pub trait EditPredictionProviderHandle {
     ) -> bool;
     fn show_completions_in_menu(&self) -> bool;
     fn show_tab_accept_marker(&self) -> bool;
+    fn supports_jump_to_edit(&self) -> bool;
     fn data_collection_state(&self, cx: &App) -> DataCollectionState;
     fn usage(&self, cx: &App) -> Option<EditPredictionUsage>;
     fn toggle_data_collection(&self, cx: &mut App);
@@ -166,6 +171,10 @@ where
         T::show_tab_accept_marker()
     }
 
+    fn supports_jump_to_edit(&self) -> bool {
+        T::supports_jump_to_edit()
+    }
+
     fn data_collection_state(&self, cx: &App) -> DataCollectionState {
         self.read(cx).data_collection_state(cx)
     }