fix(compartment-mapper/policy): do not allow "resources" to be an array

[boneskull]

closes: #1750

Description

• Disallow resources prop of a policy to be an Array
• Fix error message when defaultAttenuator is not a string (it was referencing the wrong field)
• Add tests for this and other expected behavior in assertPolicy()

Security Considerations

No

Scaling Considerations

No

Documentation Considerations

I am working on some sort of proper type declaration or schema for policies, so this will be forthcoming.

Testing Considerations

There may be more things in assertPolicy() that I missed, but I at least wanted to cover the things I changed.

Upgrade Considerations

Any policies currently in use which have a resources prop that is an Array will break.