frontbuffer enhancements to ANDROID_vulkan_native_buffer

Since VK_KHR_swapchain is implemented entirely in libvulkan, we need an
image-level mechanism to inform the driver that a swapchain image will
be used for front-buffered rendering. This is implemented by chaining
another structure off of the VkImageCreateInfo passed to the driver when
creating swapchain images.

V2: Don't foul up api file. Rerun code generators.
V3: Rename VkNativeBuffer2ANDROID structure to
VkSwapchainImageCreateInfoANDROID
V4: Provide nulldrv stub for new function
V5: rebase.

Change-Id: I4447400cb1782440638e4c8816b081dd8923ddb9
Test: compile