feat(debugger): Browse the debug console history and open diff settings from the keyboard (#162)

- Debug console: typed expressions are kept per project, and Browse Console
  History (⌥⌘E / Ctrl+Alt+E) lists them, most recent first, to put one back
  into the input.
- Diff viewer: Diff Settings (⇧⌘D / Ctrl+Shift+D) opens the viewer options
  (side-by-side / unified, whitespace, highlighting, collapsing, scroll sync)
  as a popup menu.

src/features/vcs/diffNavigator.ts

@@ -8,6 +8,8 @@ export interface DiffNavigator {
   applyChange(source: "a" | "b"): boolean;
   /** Open the next / previous file of the diff chain (changes of a commit or change list). */
   file(dir: 1 | -1): void;
+  /** The viewer's settings as a popup menu (⇧⌘D). */
+  showSettings(): void;
 }
 
 let focused: DiffNavigator | null = null;