Un-scale output distances

[achirkin]

Reverts the scaling of input data and queries that normally happens for int8/uint8 types before distance computation.
Reuses the ivf-pq post-processing step for that.

Along the way, replaces the custom fragment_scale helper with the utils::mapping that is shared among several ANN methods.

Solves #1457

[tfeher]

Thanks Artem for the fix, just a minor thing, otherwise it looks good to me.

Tagging @enp1s0 for visibility.

[cjnolet]

/merge

[ahendriksen]

It looks like this PR increased the binary size of raft_conda_cpp_cuda11_x86_64.tar.gz by 100MB (from 650MB to 750MB).
See:

• This PR: https://downloads.rapids.ai/ci/raft/branch/branch-23.06/2014112/
• Previous PR: https://downloads.rapids.ai/ci/raft/branch/branch-23.06/f60fb79/

Does anybody understand why? It is a significant enough change that might be worth investigating.

EDIT: I just noticed that the binary sizes of the rapids-nightly channel are substantially smaller (~250MB). This might be due to bz2 compression.

[achirkin]

The archives contain tests, right? We add two more sets of instantiations to cagra in tests here, which is a lot (also see #1459). Hopefully, #1428 will improve this?

[ahendriksen]

Ah yes, that makes sense. I also don't see an increase in the wheels. Thanks for pointing out!