`st/strip-extra-keys-transformer` not handling merged `s/or`

[kolstae]

Similar to #178 and might be related to #264

When having a spec with merge of an or-spec, st/strip-extra-keys-transformer removes too many keys. However it seems to be an issue with parsing of the specs.

(ns merged-or.test
  (:require [clojure.spec.alpha :as s]
            [spec-tools.core :as st]))

(s/def ::a int?)
(s/def ::doors int?)
(s/def ::wheels int?)
(s/def ::car (s/keys :req-un [::doors]))
(s/def ::bike (s/keys :req-un [::wheels]))
(s/def ::vehicle (s/or :car ::car
                       :bike ::bike))
(s/def ::merged-or (s/merge ::vehicle
                            (s/keys :opt-un [::a])))
(s/def ::merged-or-reversed (s/merge (s/keys :opt-un [::a])
                                     ::vehicle))

(let [chevy {:doors 4 :a 1}]
  [(st/coerce ::merged-or chevy st/json-transformer)
   (st/coerce ::merged-or chevy st/strip-extra-keys-transformer)
   (st/coerce ::merged-or-reversed chevy st/strip-extra-keys-transformer)])
; => [{:doors 4, :a 1}
;     {:a 1}
;     {:doors 4, :a 1}]

I've not been able to create a fix :(