Implement Arbitrary for PhantomData and PhantomPinned

[zhassan-aws]

Description of changes:

Implement Arbitrary for std::marker::PhantomData and std::marker::PhantomPinned to facilitate using #[derive(Arbitrary)] for structs containing either of them.

Resolved issues:

Resolves #2224

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

Testing:

• How is this change tested? Two new tests

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.