Add runtime schema validation for things that can't be checked by JSONSchema

* [x] a property can't be readOnly and writeOnly.
* [x] a property can't be readOnly and createOnly.
* [x] an identifier must be either createOnly or readOnly (note: this one is debatable, but CFN does not currently support updating the physicalResourceId)
* [ ] ensure that jsonPointers map to actual properties

__Update (3/16/2020)__
* [ ] [Ensure `primaryIdentifier` can only refer to a property which itself is a String or Number.](https://github.com/aws-cloudformation/cloudformation-resource-schema/issues/98)
* [ ] Ensure the property defined in `primaryIdentifier` exists

Please add more as we come across them

Review the issue checklist and the existing runtime schema-validation entry point, focusing on jsonPointers, primaryIdentifier, and the listed property constraints. Done means the selected validations are enforced and covered for valid and invalid schemas.

Written by the indexing model from the issue text.