Feature request: Making ad webviews "inspectable".

[Eric Slosser]

Apple has changed how we grant Safari access to the webviews in iOS apps. See HERE.

A side-effect is that the webview inside of GADBannerView isn't seen by Safari, unless you look in the GADBannerView's subviews, locate the WKWebView, and call `isInspectable = true` on it.

That is trickier than it sounds because the WKWebview isn't created at the time that a GADBannerViewDelegate's bannerViewDidReceiveAd is called. So inelegant solutions like polling and swizzling ensue.

To avoid this ersatz solutions, I would like the GMA-SDK to support a method to request inspectability.

The reason we need inspectability is to enable debugging and reporting misbehaving ads.