dEQP-VK.sparse_resources.shader_intrinsics*gather: fix possible of-by-one errors

dEQP-VK.sparse_resources.shader_intrinsics*gather: fix possible of-by-one errors

The test seems to perform GATHER sampling from center of pixels

On un-even image sizes this may cause failures, as texcoord (being float32)
may not exactly represent pixel center, what can cause different 2x2 rectangle to
be gathered.

The fix is to bias texcoord by half a texel, so sampling is always performed
from centre of 2x2 rectangle.

Fixes following tests (for me):
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r32i.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r32i.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r16i.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r16i.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r8i.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.r8i.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba32ui.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba32ui.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba16ui.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba16ui.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba8ui.503_137_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_sparse_gather.rgba8ui.11_37_1
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r32i.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r32i.11_37_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r16i.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r16i.11_37_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r8i.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.r8i.11_37_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba32ui.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba32ui.11_37_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba16ui.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba16ui.11_37_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba8ui.503_137_3
dEQP-VK.sparse_resources.shader_intrinsics.2d_array_sparse_gather.rgba8ui.11_37_3

Affects: dEQP-VK.sparse_resources.shader_intrinsics.*gather*

Change-Id: I218d68033e3c83d5270c54731eac3a72c6899173