Support reference lint-as macros that can be used in lint-as e.g. to support orchestra.core/defn-spec

[borkdude]

E.g. to support orchestra.core/defn-spec:

(defn-spec my-inc integer?
  [a integer?] ; Each argument is followed by its spec.
  (+ a 1))

we might support a non-existing imaginary reference macro clj-kondo.lint-as-macros/defn-1 which:

• knows that a var is being created with a certain name
• doesn't create warnings for the rest of the body, but does lint usages, so e.g. no warnings will pop up for an unused private function)

This approach might also work for the Rum macros described in #536 .