Move Hashers to util/hasher.{cpp/h}
Summary:
Move the hashers that we use for hash tables to a common place.
Moved hashers:
- SaltedTxidHasher
- SaltedOutpointHasher
- FilterHeaderHasher
- SignatureCacheHasher
- BlockHasher
Backport of core#19335 [1/3]
https://github.com/bitcoin/bitcoin/pull/19935/commits/95e61c1cf2a91d041c8025306ba36f0ea2806894
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D12149