Allow annotation keys to be Cedar reserved words

[cdisselkoen]

Description of changes

Allows annotation keys to be Cedar reserved words. Tests that this works both for human-format and JSON-format (EST) policies. Fixes #623.

Issue #, if available

#623

Checklist for requesting a review

The change in this PR is (choose one, and delete the other options):

• A bug fix or other functionality change requiring a patch to cedar-policy.

I confirm that this PR (choose one, and delete the other options):

• Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).

I confirm that cedar-spec (choose one, and delete the other options):

• Does not require updates because my change does not impact the Cedar Dafny model or DRT infrastructure.

(is that right?)

Disclaimer

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[john-h-kastner-aws]

This seems reasonable, but introduces another flavor of inconsistency in how we handle reserved identifiers.

Eliminating reserved identifiers as much as possible in other locations could be a good path towards consistency here. Probably worth discussing further.

[khieta]

Looks fine to me. I don't see a problem with allowing reserved words to be identifiers.

Edit: Agreed with @john-h-kastner-aws's comment above that it might be nice to use AnyId in other places where we currently use Id (not sure exactly where those places are, since I haven't looked at the code too recently). File an issue?

[cdisselkoen]

Opened #635 for the follow-up. Unless @john-h-kastner-aws thinks this is important to address now (before merging)?

[john-h-kastner-aws]

I think we can merge this now