Add helpers to easily read and write a serializable type to JSON

[DanilaFe]

Resolves #8278.

This PR adds methods to convert types to and from JSON strings. These serve as convenience wrappers for the existing JSON (de)serialization functionality implemented by @benharsh in #22437.

use IO, JSON;

record myPair : serializable {
  var x: int;
  var y: string;
}

var myValue = new myPair(1, "hello");
var myValueJson = toJson(myValue);

writeln(myValueJson);
writeln(fromJson(myValueJson, myPair));

Prints:

{"x":1, "y":"hello"}
(x = 1, y = hello)

Reviewed by @jeremiah-corrado -- thanks!

Testing

• paratest

[jeremiah-corrado]

looks good!

[jeremiah-corrado]

these values are unused, should they be removed from this test?

[DanilaFe]

Good catch, they should be.

[bradcray]

I don't know much about JSON, but this seems very cool and productive from a distance, thanks!