Have more inferface / classes that are disposable extend IDisposable

This makes it easier to track which objects are disposable, since we can use findAllReferences on them

src/vs/base/browser/dom.ts

@@ -905,10 +905,9 @@ export const EventHelper = {
 	}
 };
 
-export interface IFocusTracker {
+export interface IFocusTracker extends Disposable {
 	onDidFocus: Event<void>;
 	onDidBlur: Event<void>;
-	dispose(): void;
 }
 
 export function saveParentsScrollTop(node: Element): number[] {