Refactor parser, and extend for validation CAT queries

[aew]

Includes:

• Refactor parser namespace to be more concise and avoid repetition
• Extend parser to work for string formatting of Validation CAT queries (mostly whitespace)
• Simplify parsed representation for argument to be keys and values in a map
• Rename :innerType to :inner-type for consistency
• Extract test-helpers for CAT tests
• Add https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/validation/DefaultValuesOfCorrectType.yaml
• Add https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/validation/validation.schema.graphql and extract from parser test to avoid duplication

[tendant]

Thanks a lot for your contribution. I have squashed and merged all commits to avoid too many "merge" commits.