Allocate and present separate top/bottom screen framebuffer images

Instead of operating directly on the swapchain images, we have our own
top/bottom framebuffer images that will be rendered to independent of
having an available swapchain. The images are blitted into the swapchain
images, allowing for resizing too!

include/renderer_vk/renderer_vk.hpp

@@ -37,6 +37,8 @@ class RendererVK final : public Renderer {
 	// Todo: make this a configuration option
 	static constexpr usize frameBufferingCount = 3;
 
+	vk::UniqueDeviceMemory framebufferMemory = {};
+
 	// Frame-buffering data
 	// Each vector is `frameBufferingCount` in size
 	std::vector<vk::UniqueCommandBuffer> frameCommandBuffers = {};
@@ -44,6 +46,9 @@ class RendererVK final : public Renderer {
 	std::vector<vk::UniqueSemaphore> renderFinishedSemaphore = {};
 	std::vector<vk::UniqueFence> frameFinishedFences = {};
 
+	std::vector<vk::UniqueImage> topScreenImages = {};
+	std::vector<vk::UniqueImage> bottomScreenImages = {};
+
 	// Recreate the swapchain, possibly re-using the old one in the case of a resize
 	vk::Result recreateSwapchain(vk::SurfaceKHR surface, vk::Extent2D swapchainExtent);