This PR moves our fuzzers from tests/fuzzers into whatever their respective 'native' package is.
The historical reason why they were placed in an external location, is that when they were based on go-fuzz, they could not be "hidden" via the _test.go prefix. So in order to shove them away from the go-ethereum "production code", they were put aside.
But now we've rewritten them to be based on golang testing, and thus can be brought back. I've left (in tests/) the ones that are not production (bls128381), require non-standard imports (secp requires btcec, bn256 requires gnark/google/cloudflare deps).
This PR also adds a fuzzer for precompiled contracts, because why not.
This PR utilizes a newly rewritten replacement for go-118-fuzz-build, namely gofuzz-shim, which utilises the inputs from the fuzzing engine better.
Gollvm has very aggressive dead code elimination that completely
removes one of these two benchmarks. To prevent this, use the
result of the benchmark (a boolean), and to be "fair", make the
transformation to both benchmarks.
To be reliably assured of not removing the code, "use" means
assigning to an exported global. Non-exported globals and
//go:noinline functions are possibly subject to this optimization.
