Improve error messages for invalid input types

[jturkel]

Error messages when recursively validating a field argument's type don't actually include the input type's name which makes them a bit confusing. Consider the following invalid schema:

type MyType {
  myField(myArg: MyInput)
}

input MyInput {
  # This input field is invalid because it has an output type
  someInput: MyOtherType
}

type MyOtherType {
  foo: String
}

This generates the following error message that doesn't mention the MyInput type:

Argument myArg on MyType.myField is invalid: argument "someInput" type must be a valid input type (Scalar or InputObject), not GraphQL::ObjectType (MyOtherType)

With the proposed changes the error message becomes:

MyInput is invalid: argument "someInput" type must be a valid input type (Scalar or InputObject), not GraphQL::ObjectType (MyOtherType)

[rmosolgo]

👍 This change is good by me, I just want to point out that it won't apply to class-based types using the interpreter (which will someday be the only way to run graphql-ruby). I don't think it uses traversal.rb in that case. I recently added #3120 for a similar case, but maybe you're still using .define?

[jturkel]

Doh. I first noticed the problem when adding validation that deprecated arguments aren't required in #3015. The tests in question use the new class based API but I guess many of them call GraphQL::Schema.graphql_definition which triggers the legacy validation. I can't wait till the legacy APIs are removed in 2.0 😄

I'm going to close this PR since we're not using the legacy API. I'll open up a new PR that properly handles validation of required deprecated arguments in the class based API.