[pretty_format_json] Add compact array feature

[adithyabsk]

• Find non-nested numeric arrays using JSON spec: https://www.json.org/json-en.html

Note: in the process of testing this patch, I noticed that we have a round trip related bug when using json.loads followed by json.dump when dealing with small numbers (which get converted to scientific notation) and some scientific notation numbers that get converted to numbers which is undesirable, but of scope of this change.

[asottile]

please discuss features before wasting time on them

I cannot accept a regex hack unfortunately and I don't think this is a good idea anyway -- invites more bikeshedding

[adithyabsk]

please discuss features before wasting time on them

Upstream was a curtesy, plan to use the fork to unblock myself. Understand if you cannot accept the change.

If you have suggestions on a better approach, I'm open to changing the implementation (to a more mergable version). My use case was that I had some configs that were numeric array heavy that needed to be human readable. The default behavior made the json file too big.

I noticed that we have a round trip related bug

Spent some time to see if there were round trip stable json parsers but came up short. simplejson may be an option, but I didn't try it.