GPU_d3d12: Switched the default swapchain scaling mode to none.

Since there is no option to change it this seems like a much better default value. The stretching behaviour is really off-putting.

The new behavior shows a small black border when resizing the windows. This makes it more in line with the other backends and it's what you would expect to happen as a user.

src/gpu/d3d12/SDL_gpu_d3d12.c

@@ -6735,7 +6735,7 @@ static bool D3D12_INTERNAL_CreateSwapchain(
     swapchainDesc.SampleDesc.Quality = 0;
     swapchainDesc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
     swapchainDesc.BufferCount = windowData->swapchainTextureCount;
-    swapchainDesc.Scaling = DXGI_SCALING_STRETCH;
+    swapchainDesc.Scaling = DXGI_SCALING_NONE;
     swapchainDesc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
     swapchainDesc.AlphaMode = DXGI_ALPHA_MODE_UNSPECIFIED;
     swapchainDesc.Flags = 0;