Queue texel buffer dynamic indexing and texel buffer alignment requirements for VK_KHR_maintenance5

Such basic functionality missed from Vulkan core should not be spread among non-KHR extensions.

Texel buffer dynamic indexing is [acknowledged to be missing](https://github.com/KhronosGroup/Vulkan-Docs/issues/952#issuecomment-482982736) from the core Vulkan by an oversight, I think it must be queued for inclusion in the future VK_KHR_maintenance4 extension.

I also don't think VK_EXT_texel_buffer_alignment is vendor specific, I think it should go to VK_KHR_maintenance4 as well.

No file, test, or entry point is named. Start by reviewing the linked Vulkan-Docs discussion and the VK_KHR_maintenance4 and VK_EXT_texel_buffer_alignment requirements; done would require a resolved decision about where these requirements belong.

Written by the indexing model from the issue text.