refactor: Move fs.* to util/fs.*
Summary:
The fs.* files are already part of the libbitcoin_util library. With the
introduction of the fs_helpers.* it makes sense to move fs.* into the
util/ directory as well.
This concludes backport of core#27254
https://github.com/bitcoin/bitcoin/pull/27254/commits/00e9b97f37e0bdf4c647236838c10b68b7ad5be3
Depends on D16153
Test Plan:
With Chronik and bitcoin chainstate
ninja all check-all bench-bitcoin bitcoin-fuzzers
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16154