Export AppBase class to allow testing by external applications (#4183)

Co-authored-by: Martin Valigursky <mvaligursky@snapchat.com>

src/index.js

@@ -211,7 +211,7 @@ export { getTouchTargetCoords, Touch, TouchEvent } from './input/touch-event.js'
 // FRAMEWORK
 export * from './framework/constants.js';
 export { script } from './framework/script.js';
-export { app } from './framework/app-base.js';
+export { AppBase, app } from './framework/app-base.js';
 export { Application } from './framework/application.js';
 export { AnimationComponent } from './framework/components/animation/component.js';
 export { AnimationComponentSystem } from './framework/components/animation/system.js';