De-duplicate code for checking if entity types exist in schema

[john-h-kastner-aws]

Describe the improvement you'd like to request

The human-readable schema format included some duplicate checks that check for the existence of an entity type when it is used in a schema. This checks is already done when construct a ValidatorSchema object, so it shouldn't be necessary to also perform the check when parsing the schema.

Describe alternatives you've considered

No response

Additional context

No response

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this internal improvement
• ⚠️ This feature might incur a breaking change

[memark]

Is this issue about refactoring out duplicate code to a common place, or to remove one of the duplicate checks altogether?

[john-h-kastner-aws]

It's not obvious what exactly this would entail.

The human-readable parser has to deal with issues around collisions between names for entity/builtin/extension/common types that JSON schema doesn't need to care about, so there's going to be some code exclusively used by the human schema parser. @shaobo-he-aws probably knows that relevant code best.