Dispose events

https://github.com/microsoft/vscode/issues/155232

The events that is setup for needs to be disposed for js to be able
to garbage collect the terminals.

src/browser/Linkifier2.ts

@@ -38,6 +38,13 @@ export class Linkifier2 extends Disposable implements ILinkifier2 {
     this.register(getDisposeArrayDisposable(this._linkCacheDisposables));
   }
 
+  public dispose(): void {
+    super.dispose();
+    this._onShowLinkUnderline.dispose();
+    this._onHideLinkUnderline.dispose();
+    this._lastMouseEvent = undefined;
+  }
+
   public registerLinkProvider(linkProvider: ILinkProvider): IDisposable {
     this._linkProviders.push(linkProvider);
     return {