Schema validation: objects

[ghostdogpr]

In Validator.validateSchema, verify the rules for object types

1. An Object type must define one or more fields.
2. For each field of an Object type:
   1. The field must have a unique name within that Object type;
      no two fields may share the same name.
   2. The field must not have a name which begins with the
      characters {"__"} (two underscores).
   3. The field must return a type where {IsOutputType(fieldType)} returns {true}.
   4. For each argument of the field:
      1. The argument must not have a name which begins with the
         characters {"__"} (two underscores).
      2. The argument must accept a type where {IsInputType(argumentType)}
         returns {true}.
3. An object type may declare that it implements one or more unique interfaces.
4. An object type must be a super-set of all interfaces it implements:
   1. The object type must include a field of the same name for every field
      defined in an interface.
      1. The object field must be of a type which is equal to or a sub-type of
         the interface field (covariant).
         1. An object field type is a valid sub-type if it is equal to (the same
            type as) the interface field type.
         2. An object field type is a valid sub-type if it is an Object type and
            the interface field type is either an Interface type or a Union type
            and the object field type is a possible type of the interface field
            type.
         3. An object field type is a valid sub-type if it is a List type and
            the interface field type is also a List type and the list-item type
            of the object field type is a valid sub-type of the list-item type
            of the interface field type.
         4. An object field type is a valid sub-type if it is a Non-Null variant
            of a valid sub-type of the interface field type.
      2. The object field must include an argument of the same name for every
         argument defined in the interface field.
         1. The object field argument must accept the same type (invariant) as
            the interface field argument.
      3. The object field may include additional arguments not defined in the
         interface field, but any additional argument must not be required, e.g.
         must not be of a non-nullable type.

[zalbia]

Working on this if someone isn't already.