Scalar layouts for uniform buffers

The [descriptor pool](https://docs.vulkan.org/tutorial/latest/05_Uniform_buffers/01_Descriptor_pool_and_sets.html) chapter of the new vulkan tutorial uses std430 as the uniform buffer layout. Scalar layout is basically universally available at this point and matches C++ alignment much better (assuming no vector types), are there any deeper reasons for why the tutorial couldn't use it?

Start with the linked descriptor pool chapter and identify where it specifies or relies on std430 for uniform buffers. Check the Vulkan requirements and the tutorial's C++ alignment assumptions for scalar layout. Done means the chapter either adopts scalar layout with the necessary explanation or documents why std430 remains preferable.

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