Fixed Vulkan validation error in SDL_RenderReadPixels()

  Validation Error: [ VUID-VkImageMemoryBarrier-oldLayout-01212 ] | MessageID = 0xff795e16
  vkCmdPipelineBarrier(): pImageMemoryBarriers[0].newLayout (VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL) is not compatible with VkImage 0x2160000000216 usage flags VK_IMAGE_USAGE_2_TRANSFER_DST_BIT_KHR|VK_IMAGE_USAGE_2_COLOR_ATTACHMENT_BIT_KHR.
  The Vulkan spec states: If layouts are not ignored, oldLayout or newLayout is VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL then image must have been created with the VK_IMAGE_USAGE_TRANSFER_SRC_BIT usage flag set (https://docs.vulkan.org/spec/latest/chapters/synchronization.html#VUID-VkImageMemoryBarrier-oldLayout-01212)

src/render/vulkan/SDL_render_vulkan.c

@@ -2312,6 +2312,10 @@ static VkResult VULKAN_CreateSwapChain(SDL_Renderer *renderer, int w, int h)
     swapchainCreateInfo.imageExtent = rendererData->swapchainSize;
     swapchainCreateInfo.imageArrayLayers = 1;
     swapchainCreateInfo.imageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT;
+    // SDL_RenderReadPixels() copies from the swapchain image, which requires TRANSFER_SRC
+    if (rendererData->surfaceCapabilities.supportedUsageFlags & VK_IMAGE_USAGE_TRANSFER_SRC_BIT) {
+        swapchainCreateInfo.imageUsage |= VK_IMAGE_USAGE_TRANSFER_SRC_BIT;
+    }
     swapchainCreateInfo.imageSharingMode = VK_SHARING_MODE_EXCLUSIVE;
     swapchainCreateInfo.preTransform = rendererData->swapChainPreTransform;
     swapchainCreateInfo.compositeAlpha = (renderer->window->flags & SDL_WINDOW_TRANSPARENT) ? (VkCompositeAlphaFlagBitsKHR)0 : VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;