This removes the old getClientExtent stuff that I added a while back,
and replaces it with the strategy espoused by the MoltenVK author found
here:
https://github.com/KhronosGroup/MoltenVK/issues/428
I tested this PR on macOS with Vulkan and Metal. I tested both on high
and low DPI displays. I also tried dragging the window between the two
displays.
Android still has issues with rotation, I will deal with that next.
cleanup
fb8c51c5e1