Add LazyJSONDocument, which wraps a JSON string and only deserializes it if needed.

[nicktobey]

This is the GMS side of dolthub/dolt#7749

This is a new JSONWrapper implementation. It isn't used by the GMS in-memory storage, but it will be used in Dolt to speed up SELECT queries that don't care about the structure of the JSON.

A big difference between this and JSONDocument is that even after it de-serializes the JSON into a go value, it continues to keep the string in memory. This is good in cases where we would want to re-serialize the JSON later without changing it. (So statements like SELECT json FROM table WHERE json->>"$.key" = "foo"; will still be faster.) But with the downside of using more memory than JSONDocument)

[nicktobey]

One detail to note is that we currently desalinize JSON prior to writing it on the wire, so that we can re-serialize it in a way that matches MySQL's output (different whitespacing.) This is expensive and I don't think is worth it.

I discussed with Max whether or not we consider it a requirement to match MySQL's wire responses exactly for JSON, and agreed that we could probably relax that requirement. With this change, casting a document to a text type will still result in the same output as MySQL, but simply displaying it in a query result won't.

[fulghum]

Looks good. It seems reasonable to tradeoff fully matching the whitespace formatting in MySQL's JSON output, with getting faster performance.