Add Android P cutout (aka notch) support

[mars3142]

I just want to add a reminder, that Android P will support natively cutouts and every game, which target is below P will have reduced screen sizes.

So the framework should be Android P ready, if the final SDK will be released and someone can upload new and updated apps to the PlayStore.

[piotrros]

Maybe we can use Director::getSafeAreaRect() for it?

[mars3142]

We should use it, but the current targetSDK isn't an integer, so it can't included into the v3 branch until the Android P SDK is final.

[mars3142]

Since yesterday the Android API 28 is final, so we are able to implement it into the framework.

[gestern]

Guys, I've implemented this functionality for Android (Including deep support of Android P), the details will be later, now I'm testing on devices

[drelaptop]

thanks for @gestern contribution, refer to #19043 discuss if you have doubt.

[formatCvt]

hmm, looks like only rounded corners support added not cutout