This PR will remove the filtering when gathering texels for HiZ. The
algorithm that we follow doesn't use it, but had issues when
implementing using textureGather where he mentioned that he needed to
enable filtering.
```
I was experimenting with using texture gather lookups to reduce
the number of texture fetches from 4-to-7 fetches per fragment
down to 1-to-3 fetches per fragment (see the extension
ARB_texture_gather) it seems that texture gather works only if
the image is linearly sampled and to avoid the additional burden
involved by switching filtering state during rendering I stuck
to simple texture lookups as using texture gather lookups did not
show any visible effect on the construction time of the Hi-Z map.
```
https://www.rastergrid.com/blog/2010/10/hierarchical-z-map-based-occlusion-culling/
After testing we got identical results when turning off filtering.
Turning off filtering allows supporting devices that don't support
linear filtering on depth stencil texture (WoA) using the Vulkan
backend.
Pull Request: https://projects.blender.org/blender/blender/pulls/139868
4a1078b3de