Support KClass.isInstance/cast/safeCast in stdlib-only reflection implementation

#KT-14720 Fixed

libraries/stdlib/src/kotlin/reflect/KClasses.kt

@@ -0,0 +1,40 @@
+/*
+ * 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.
+ */
+
+@file:kotlin.jvm.JvmName("KClasses")
+@file:Suppress("UNCHECKED_CAST")
+
+package kotlin.reflect
+
+/**
+ * Casts the given [value] to the class represented by this [KClass] object.
+ * Throws an exception if the value is `null` or if it is not an instance of this class.
+ *
+ * This is an experimental function that behaves as a similar function from kotlin.reflect.full on JVM.
+ *
+ * @see [KClass.isInstance]
+ * @see [KClass.safeCast]
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+fun <T : Any> KClass<T>.cast(value: Any?): T {
+    if (!isInstance(value)) throw ClassCastException("Value cannot be cast to $qualifiedName")
+    return value as T
+}
+
+/**
+ * Casts the given [value] to the class represented by this [KClass] object.
+ * Returns `null` if the value is `null` or if it is not an instance of this class.
+ *
+ * This is an experimental function that behaves as a similar function from kotlin.reflect.full on JVM.
+ *
+ * @see [KClass.isInstance]
+ * @see [KClass.cast]
+ */
+@SinceKotlin("1.3")
+@ExperimentalStdlibApi
+fun <T : Any> KClass<T>.safeCast(value: Any?): T? {
+    return if (isInstance(value)) value as T else null
+}