yaml.v3: add FuzzEncodeFromJSON which signals roundtripping issues

[dolmen]

gopkg.in/yaml.v3 has roundtripping bugs that I have demonstrated using a fuzzer in go-yaml/yaml#1028. But that module looks unmaintained while it has a key position in the Go ecosystem. Cc: @niemeyer

I'm resubmitting this fuzzer here in hope it will get more attention here (well, hopefully not just from black hats).

$ go test -fuzz F
OK: 50 passed
fuzz: elapsed: 0s, gathering baseline coverage: 0/9 completed
fuzz: elapsed: 0s, gathering baseline coverage: 9/9 completed, now fuzzing with 8 workers
fuzz: elapsed: 0s, execs: 8702 (34591/sec), new interesting: 45 (total: 54)
--- FAIL: FuzzEncodeFromJSON (0.26s)
    --- FAIL: FuzzEncodeFromJSON (0.00s)
        fuzz_test.go:33: JSON "-0"
        fuzz_test.go:34: Go   %!q(float64=-0) <-0x0p+00>
        fuzz_test.go:41: YAML "-0\n" <2d300a>
        fuzz_test.go:49: Go   '\x00' <0>
        fuzz_test.go:62: YAML "0\n" <300a>
        fuzz_test.go:65: Marshal->Unmarshal->Marshal mismatch:
            - expected: "-0\n"
            - got:      "0\n"
    
    Failing input written to testdata/fuzz/FuzzEncodeFromJSON/c64b69bf2c432100
    To re-run:
    go test -run=FuzzEncodeFromJSON/c64b69bf2c432100
FAIL
exit status 1
FAIL	sigs.k8s.io/yaml/goyaml.v3	4.082s

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