Move util files to directory
Summary: This is a remake of Core PR14555, but due to codebase divergence, I redid it from scratch.
Test Plan:
make check ninja check
Also ran the ross compilation builds.
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D4131