[FEA] Remove PqBits as a template of IVF-PQ code

Currently IVF-PQ is using PqBits as a template. Switching that to a run-time parameter could reduce compilation time and the total library size.
PR #1278 introduced a version of `bitfield_ref_t` and `bitfield_view_t` that doesn't require PqBits as a template so that can be re-used when needed in IVF-PQ.