IR JS: support findAssociatedObject feature (KT-37418 fixed)

libraries/stdlib/js-v1/src/kotlin/reflection_js-v1.kt

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+import kotlin.reflect.KClass
+
+@PublishedApi
+internal fun <T : Annotation> KClass<*>.findAssociatedObject(annotationClass: KClass<T>): Any? {
+    // This API is not supported in js-v1. Return `null` to be source-compatible with js-ir.
+    return null
+}