Necessary to get the name of the type when
the underlying type may not exist in the schema
and therefore `Absinthe.Type.name/1` won't work.

spec: https://spec.graphql.org/October2021/#sec-All-Variable-Usages-are-Allowed

fixes absinthe-graphql#1134

Several cases did not return errors
 * when the location type was non nullable and the variable nullable
 * when the location type was a list and the variable wasn't

Some cases are allowed:
  * contravariant, when the location type is nullable and the variable
    non-nullable
  * the the argument is non-nullable but either the variable or argument
    has a default value

With the changes on allowed variable usage they would only test
whether the directive variable in the operation was present. This
is covered elsewhere.