anv: Implement VK_EXT_texel_buffer_alignment

This MR implements the new VK_EXT_texel_buffer_alignment extension. The current alignment we are exposing in the driver is correct for uniform texel buffers but wrong for storage texel buffers and can potentially lead to hangs. The last commit in the MR corrects our current advertisement to 16B which is the worst-case for storage texel buffers.

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