Fixes for Android Delphi/Stencil buffer problems.

It appears on some newer devices (Nexus 4) the defaults used by the AndroidGameView result in a surface without a depth or stencil buffer. This PR corrects the issue by attempting to use the PreferredDepthStencilFormat to pass in the correct parameters that the user wants. 

Also fixes an issue in the AddSpecular function in the shader 

This has been tested on 4 different devices and emulator and works ok. 

If we have the xamarin test cloud we could know for sure but hey ho ;)