Implement String to/from ByteArray conversion (KT-24810)

libraries/stdlib/js/test/core/testUtils.kt

@@ -13,3 +13,7 @@ public actual fun assertTypeEquals(expected: Any?, actual: Any?) {
 
 @Suppress("NOTHING_TO_INLINE")
 internal actual inline fun String.removeLeadingPlusOnJava6(): String = this
+
+internal actual inline fun testOnNonJvm6And7(f: () -> Unit) {
+    f()
+}

libraries/stdlib/js/test/text/StringEncodingTestJs.kt

@@ -0,0 +1,11 @@
+/*
+ * Copyright 2010-2019 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.
+ */
+
+package test.text
+
+
+internal actual val surrogateCodePointDecoding: String = "���"
+
+internal actual val surrogateCharEncoding: ByteArray = byteArrayOf(0xEF.toByte(), 0xBF.toByte(), 0xBD.toByte())