CLJS-2790: Externs inference warnings for defrecord fields

Applies the same solution to supress access to the other object's
__extmap in the IEquiv implementation (adding a type tag) to generated
accessors to the other object's fields.

Author: mfikes

src/main/clojure/cljs/core.cljc

@@ -1816,7 +1816,7 @@
                                               (.-constructor ~other))
                                   ~@(map (core/fn [field]
                                            `(= (.. ~this ~(to-property field))
-                                               (.. ~other ~(to-property field))))
+                                               (.. ~(with-meta other {:tag tagname}) ~(to-property field))))
                                          base-fields)
                                   (= (.-__extmap ~this)
                                      (.-__extmap ~(with-meta other {:tag tagname}))))))

src/test/clojure/cljs/analyzer_tests.clj

@@ -1096,3 +1096,14 @@
                :with-core? true})]
     (is (empty? @ws))
     (is (not (string/includes? res "cljs.core")))))
+
+(deftest test-cljs-2790-defrecord-fields
+  (let [ws  (atom [])
+        res (infer-test-helper
+              {:forms '[(ns cjls-2790.core)
+                        (defrecord Foo [a b])]
+               :externs ["src/test/externs/test.js"]
+               :warnings ws
+               :with-core? true})]
+    (is (empty? @ws))
+    (is (not (string/includes? res "cljs.core")))))