MSL: Support option for treating 1D textures as 2D textures of height 1.
MSL: Support option for treating 1D textures as 2D textures of height 1.

Fixes from feedback.

Change vertical sampling of 1D texture from 0.0 to 0.5 to avoid edge conditions.

KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross,KhronosGroup/SPIRV-Cross