[JS IR BE] Add a few kotlin.test stubs to IR runtime

compiler/testData/codegen/box/ranges/contains/inRangeWithSmartCast.kt

@@ -1,4 +1,4 @@
-// IGNORE_BACKEND: JS_IR, NATIVE
+// IGNORE_BACKEND: NATIVE
 // WITH_RUNTIME
 import kotlin.test.assertTrue
 

compiler/testData/codegen/box/reflection/noReflectAtRuntime/simpleClassLiterals.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: NATIVE
 
 // WITH_RUNTIME

libraries/stdlib/js/irRuntime/tests.kt

@@ -5,7 +5,23 @@
 
 package kotlin.test
 
+// This file plugs some declaration from "kotlin.test" library used in tests.
+
 fun <T> assertEquals(a: T, b: T) {
     if (a != b) throw Exception("")
 }
 
+fun assertTrue(x: Boolean) {
+    if (!x) throw Exception("")
+}
+
+fun assertFalse(x: Boolean) {
+    if (x) throw Exception("")
+}
+
+fun <T : Any> assertNotNull(actual: T?, message: String? = null): T {
+    if (actual == null) throw Exception("")
+    return actual
+}
+
+