adds PolicySet to JSON conversion

[muditchaudhary]

Overview

Implements JSON conversion support for CedarJava, allowing PolicySet objects to be converted to Cedar's JSON format, similar to the to_json() functionality in the cedar_policy Rust library.

Changes

• Adds .toJson method for PolicySet to convert PolicySet to Cedar JSON format
• Adds tests for both Java and FFI
• Improves test output clarity by adding env.exception_clear().unwrap()

Example Usage

EntityTypeName principalType = EntityTypeName.parse("User").get();
Set<Policy> policies = new HashSet<>();
Set<Policy> templates = new HashSet<>();
ArrayList<TemplateLink> templateLinks = new ArrayList<TemplateLink>();
ArrayList<LinkValue> linkValueList = new ArrayList<>();

String fullPolicy =
        "permit(principal == User::\"Bob\", action == Action::\"View_Photo\", resource in Album::\"Vacation\");";
Policy newPolicy = new Policy(fullPolicy, "p1");
policies.add(newPolicy);

String template = "permit(principal == ?principal, action == Action::\"View_Photo\", resource in Album::\"Vacation\");";
Policy policyTemplate = new Policy(template, "t0");
templates.add(policyTemplate);

Entity principal = new Entity(principalType.of("Alice"), new HashMap<>(), new HashSet<>());
LinkValue principalLinkValue = new LinkValue("?principal", principal.getEUID());
linkValueList.add(principalLinkValue);

TemplateLink templateLink = new TemplateLink("t0", "tl0", linkValueList);
templateLinks.add(templateLink);

PolicySet validPolicySet = PolicySet(policies, templates, templateLinks)

String validPolicySetJson = validPolicySet.toJson()