validate oneOf input objects in lists coerced from non-array values - #4494

with input OneOf @oneOf { a: Int, b: Int } and type Query { q(oneofs: [OneOf]): Boolean }:

{ q(oneofs: {a: null}) }
=> {"data": {"q": true}}    (no errors, the fetcher received [{a: null}])

ValuesResolverOneOfValidation.validateOneOfInputTypes only walks list elements when the argument AST node is an ArrayValue. A single object literal coerced into a list per the spec's list input coercion is never checked, and neither is a list resolved from a variable default, query ($v: [OneOf] = [{a: null}]) { q(oneofs: $v) }, because variable defaults are coerced by literalToInternalValue which does no oneOf validation. Document validation doesn't reject these either, ValidationUtil only enforces the key count. Lists sent through the variables map are unaffected, they are already checked per element in ValuesResolverConversion.

The fix validates the coerced list elements directly when the argument value is not an ArrayValue, so these inputs now fail with the same OneOfNullValueException / OneOfTooManyKeysException as their array-literal equivalents.