Make MurmurHash3 consume Spans

Summary:
Partial backport (6/8) of core PR19326:
https://github.com/bitcoin/bitcoin/pull/19326/commits/0ef97b1b103231db54e04a64bbdb5dcc3f34f482

Depends on D9151.

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9152