Dictionary validate updates

[toasted-nutbread]

This change makes dictionary-validate.js and schema-validate.js able to use https://ajv.js.org as a validator for testing.

This was originally mentioned in #2129 (comment):

I don't know anything about JSON schema validation, and I haven't looked into how Yomichan does it or what engine it uses. My naive hope was that maybe Yomichan could be updated to use a faster validator (ajv claims to be the fastest) and perhaps that would be enough to solve the problem.

[stephenmk]

My new JMdict dictionary for Yomichan validates in 3.25 seconds on my PC now -- incredible!

[toasted-nutbread]

Yeah, it's because their validator compiles to actual JavaScript code, which presents some potential challenges with integrating into Yomichan. This is a first step towards evaluating what can be done here.