fuzz: Avoid -fsanitize=integer warnings in fuzzing harnesses, add UBSan suppressions
Summary:
Notes:
- chain.h and chain.cpp were fixed and removed by us in D12816 (out of order backport)
- strencodings.* was fixed and removed by us in D12813 (out of order backport)
- we do not have a bech32.cpp file, so I removed it as well
This is a backport of core#21000
Test Plan:
With UBSAN
ninja && ninja check bitcoin-fuzzers check-functional
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D12829