Resolver parameter typed by the resolver's own type variable fails on every query #880

A resolver method inherited from a generic class, whose parameter is the class's type variable, builds fine but fails on every query.

type Query {
    generic(input: GreetingInput!): String!
    plain(input: GreetingInput!): String!
}

input GreetingInput {
    name: String!
}

data class GreetingInput(val name: String)

abstract class InputResolver<I> : GraphQLQueryResolver {
    fun generic(input: I): String = "generic got $input"
}

class GreetingQuery : InputResolver<GreetingInput>() {
    fun plain(input: GreetingInput): String = "plain got $input"
}

{ plain(input: { name: "a" }) } returns plain got GreetingInput(name=a), but { generic(input: { name: "a" }) } fails with:

Exception while fetching data (/generic) : class sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to class java.lang.Class

Same on graphql-java 26.1 and 25.1, on current master.

The scanner resolves I to GreetingInput through the type resolver, which is why the build works. The data fetcher doesn't. MethodFieldResolver#createDataFetcher keeps method.genericParameterTypes[i] as is (the ?.apply { typeResolver.getRawClass(this) } throws the resolved type away), then shouldValueBeConverted calls JavaType.unwrap(), which does this as Class<*>. ArgumentConverter is built with the unresolved I too, so I think fixing only the cast would hand the method a Map.

Not the same as #333 / #468, those were generic input classes (A<B>) failing at scan time.

Found by the every-field check in #879, which excludes Query.generic in UnmappedInputFieldsTest until this is fixed.