Schema validation: input objects

[ghostdogpr]

In Validator.validateSchema, verify the rules for input object types

1. An Input Object type must define one or more input fields.
2. For each input field of an Input Object type:
   1. The input field must have a unique name within that Input Object type;
      no two input fields may share the same name.
   2. The input field must not have a name which begins with the
      characters {"__"} (two underscores).
   3. The input field must accept a type where {IsInputType(inputFieldType)}
      returns {true}.

[mriceron]

I can work on this if no ones is

[ghostdogpr]

@mriceron sure! 👍