tests: Add fuzzing harnesses for various Base{32,58,64} and hex related functions

Summary:

Add fuzzing harnesses for various Base{32,58,64} and hex related
functions.

Backport of core PR17229.

The missing corpora change is irrelevant for us.

Depends on D8155.

Test Plan:

ninja bitcoin-fuzzers
./test/fuzz/test_runner.py <path_to_corpus>

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8156