loader: Address Jon Ashburn's review comments.
loader: Address Jon Ashburn's review comments.

It took a few commits (squashed down into 1) to get it correct.  Includes:

Use loader_heap_{alloc|free}().

Try to deal correctly with initializing the vkCreate*SurfaceKHR()'s.

KhronosGroup/Vulkan-Headers,KhronosGroup/Vulkan-Headers,KhronosGroup/Vulkan-Headers