Fix interstitial performance on some Android devices

[pablorengo]

On some devices, like Samsung J7, when showing a banner and then a interstitial, the interstitial close event has a delay of 5 seconds.

The OnGlobalLayoutListener of the bannerView is executed even if the banner is not being shown, and the update on the PopupWindows has performance issues, so moved them to the show and hide methods of the banner.

[stowy]

I have a change to banner positioning pending which I hope to release this week which may resolve this issue, so waiting on that before addressing this.