KT-2752: add checkers for inconsistent usage of JsName

js/js.translator/testData/box/nameClashes/extensionPropertyAndMethod.kt

@@ -0,0 +1,15 @@
+package foo
+
+class A
+
+fun A.bar() = 23
+
+val A.bar: Int
+    get() = 42
+
+fun box(): String {
+    assertEquals(23, A().bar())
+    assertEquals(42, A().bar)
+
+    return "OK"
+}