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/zed/src/zed/inline_completion_registry.rs

@@ -1,7 +1,7 @@
 use client::{Client, UserStore};
 use collections::HashMap;
 use copilot::{Copilot, CopilotCompletionProvider};
-use editor::{Editor, EditorMode};
+use editor::Editor;
 use gpui::{AnyWindowHandle, App, AppContext as _, Context, Entity, WeakEntity};
 use language::language_settings::{EditPredictionProvider, all_language_settings};
 use settings::SettingsStore;
@@ -18,7 +18,7 @@ pub fn init(client: Arc<Client>, user_store: Entity<UserStore>, cx: &mut App) {
         let client = client.clone();
         let user_store = user_store.clone();
         move |editor: &mut Editor, window, cx: &mut Context<Editor>| {
-            if editor.mode() != EditorMode::Full {
+            if !editor.mode().is_full() {
                 return;
             }