editor: Refactor EditorMode::Full (#28546)

This PR lightly refactors the `EditorMode::Full` exposing two new
methods: `is_full` and `set_mode`.

Motivation is to expose fields that modify the behavior when the editor
is in `Full` mode. By using is `mode.is_full()` instead of
`EditorMode::Full` we can introduce new fields without breaking other
places in the code.

Release Notes:

- N/A

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/go_to_line/src/cursor_position.rs

@@ -95,7 +95,7 @@ impl CursorPosition {
                                 cursor_position.position = None;
                                 cursor_position.context = None;
                             }
-                            editor::EditorMode::Full => {
+                            editor::EditorMode::Full { .. } => {
                                 let mut last_selection = None::<Selection<Point>>;
                                 let snapshot = editor.buffer().read(cx).snapshot(cx);
                                 if snapshot.excerpts().count() > 0 {