tests: Add fuzzing harness for locale independence testing
Summary:
Context: C and C++ locale assumptions in bitcoind and bitcoin-qt Add fuzzing harness for locale independence testing of functions in strencodings.h and tinyformat.h.
Backport of core PR18126.
Test Plan:
ninja bitcoin-fuzzers ./test/fuzz/test_runner.py <path_to_corpus>
Reviewers: #bitcoin_abc, PiRK
Reviewed By: PiRK
Differential Revision: https://reviews.bitcoinabc.org/D8251