Adds functionality to parse Entity from JSON

[muditchaudhary]

Description

1. Implements and registers EntityDeserializer for converting JSON strings into Entity objects.
2. Modifies CedarJson visibility to allow its use in a different package or module.
3. Adds two new parsing methods to the Entity class:
   • Entity.parse(String jsonString): Loads an Entity from a JSON string.
   • Entity.parse(Path filePath): Loads an Entity from a JSON file.
4. Includes unit tests for the new Entity.parse() methods.

[cdisselkoen]

Looks good. I didn't look at the tests in detail but I trust they are correct. I think we already test this functionality through the corpus tests anyway?