The definition of the froxel buffer sizes were spread across
multiple places and for different use cases (including
allocating the buffer, setting to a descriptor set, and adjusting
the relevant spec constant). In this commit, we try to unify
the size definitions into Froxelizer::getFroxelBufferByteCount().
We also remove the vulkan-only special case for froxel buffer
UBO. This case was introduced because spec constant couldn't be
used to size arrays for some drivers in the past, but we introduced a
workaround that replaced spec constants with constants.
b68e9fef03