Creates stencil and depth render buffers for OpenGL rendering.

This commit creates stencil render buffer because it's required by nanovg for rendering properly. Depth render buffer is also created to support more widely rendering purpose.

Both render buffers are created for Android, Mac, and iOS. 8-bit is used for stencil render buffer and 24-bit is used for depth render buffer for all platforms.

Signed-off-by: Olli Wang <olliwang@ollix.com>