Introduce OptionalExpectation for annotations missing on some platforms

This commits adds a new annotation OptionalExpectation to the standard
library, which is experimental. To enable its usage, either pass
'-Xuse-experimental=kotlin.ExperimentalMultiplatform' as a compiler
argument, or '-Xuse-experimental=kotlin.Experimental' and also annotate
each usage with `@UseExperimental(ExperimentalMultiplatform::class)`

 #KT-18882 Fixed

compiler/testData/codegen/box/jvmName/loadJvmName.kt

@@ -0,0 +1,13 @@
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+
+@JvmName("bar")
+fun foo() {}
+
+fun getJvmName(): JvmName? =
+        Class.forName("LoadJvmNameKt").declaredMethods.single { it.name == "bar" }.getAnnotation(JvmName::class.java)
+
+fun box(): String {
+    // JvmName is binary-retained and should not be accessible via reflection
+    return if (getJvmName() == null) "OK" else "Fail"
+}