Extend parser to pass parser CAT

[aew]

Previously, the following CAT cases were failing:

• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L14
• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L36
• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L44
• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L123
• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L139
• https://github.com/graphql-cats/graphql-cats/blob/master/scenarios/parsing/SchemaParser.yaml#L158

[tendant]

@aew Thanks for your contribution!

[tendant]

One comment:

"TypeFields*" and "TypeFields ::= TypeField | TypeField TypeFields" is ambiguous.

I might consider to use:

"TypeField*"

or

"TypeFields" and "TypeFields ::= TypeField | TypeField TypeFields"

or

"TypeFields" and "TypeFields ::= TypeField*"

I will make the change later.