Benchmark against Ajv JTD serializer

[mcollina]

🚀 Feature Proposal

Add a benchmark against Ajv JTD serializer: https://ajv.js.org/guide/getting-started.html#parsing-and-serializing-json

[mcollina]

cc @epoberezkin

[epoberezkin]

I can do it in April - thank you @mcollina

[mcollina]

Please write this against the next branch, as it already Ajv v7.