Test minimum alignment for texel buffers.

Test minimum alignment for texel buffers.

For https://gitlab.khronos.org/vulkan/vulkan/issues/1705

If VK_EXT_texel_buffer_alignment is supported, compute the alignment for the
format, else use minTexelBufferOffsetAlignment.

Always use the minimum alignment for texel buffers in shader access tests.
Add variants of image load/store tests that use single texel alignment.

Components: Vulkan
Affects: dEQP-VK.binding_model.*offset_nonzero*
Affects: dEQP-VK.image*store*buffer*

Change-Id: I160c91b8c98ee4d518924e00e02770626763934c