Adds annotation support for Policy

[muditchaudhary]

Description

This PR implements annotation getters for the Policy class, providing access to both static policy and template policy annotations.

Key Changes

• Implements a Java HashMap in CedarJavaFFI for annotation management and JNI communication
• Adds annotation access methods to Policy class:
  • getAnnotation(String key)
  • getAnnotations()
• Implements lazy loading pattern for annotations:
  • Annotations initialize via JNI only on first getter call
  • Subsequent calls utilize cached annotations
• Adds test coverage for:
  • New FFI methods
  • CedarJavaFFI HashMap implementation
  • Policy annotation getters

Implementation Details

1. Handling Static Policies and Templates

   • Uses try-catch approach to attempt static policy annotation retrieval first
   • Falls back to template annotation retrieval on failure (errorMessage.contains("expected a static policy"))
   • Current implementation relies on error message parsing (precedent in PolicyTests). Limited by information exposed by cedar-policy's ParseError (tracking in #979)
   • Alternative: Completely consume ParseError for static policies (as in PR Exposes policy effect for static policies and templates #275)
   • Temporary workaround until Policy and Template class separation

2. Lazy Loading Strategy

   • Loads annotations on-demand instead of in Policy constructor to preserve backward compatibility by avoiding addition of InternalException in constructor signature.

[mark-creamer-amazon]

Is there any reason we can't include this snippet of code that should be run once per instance in the constructor?

[muditchaudhary]

This snippet throws an InternalException, but the current constructor doesn't declare this exception. Moving this code into the constructor would require us to either add throws InternalException to the constructor signature, which would be a breaking change for existing users.

[mark-creamer-amazon]

Ah, good reason for this major version at least 👍

[john-h-kastner-aws]

looks reasonable