tests/fuzzers/bls1381: add bls fuzzer (#21796)

* added bls fuzzer

* crypto/bls12381: revert bls-changes, fixup fuzzer tests

* fuzzers: split bls fuzzing into 8 different units

* fuzzers/bls: remove (now stale) corpus

* crypto/bls12381: added blsfuzz corpus

* fuzzers/bls12381: fix the bls corpus

* fuzzers: fix oss-fuzz script

* tests/fuzzers: fixups on bls corpus

* test/fuzzers: remove leftover corpus

Co-authored-by: Marius van der Wijden <m.vanderwijden@live.de>