Fix GestureEventListeners generated externs name.

Due to some compiler weirdness, we recently added some hacky indirection
around GestureEventListeners, however this changed the name of that
mixin from Analyzer's perspective by adding a leading underscore. This
fixes that.

lib/mixins/gesture-event-listeners.js

@@ -27,7 +27,7 @@ import { addListener, removeListener } from '../utils/gestures.js';
  *   cross-platform
  * gesture events to nodes
  */
-const _GestureEventListeners = dedupingMixin(
+const GestureEventListeners = dedupingMixin(
     /**
      * @template T
      * @param {function(new:T)} superClass Class to apply mixin to.
@@ -74,13 +74,15 @@ const _GestureEventListeners = dedupingMixin(
       return GestureEventListeners;
     });
 
-// Somehow _GestureEventListeners is incorrectly typed as *. For now add this
+// Somehow GestureEventListeners is incorrectly typed as *. For now add this
 // cast.
 /**
  * @template T
  * @param {function(new:T)} superClass Class to apply mixin to.
  * @return {function(new:T)} superClass with mixin applied.
  */
-export const GestureEventListeners = function(superClass) {
-  return _GestureEventListeners(superClass);
+const _GestureEventListeners = function(superClass) {
+  return GestureEventListeners(superClass);
 };
+
+export {_GestureEventListeners as GestureEventListeners};