[Tests] Migrate backend-independent tests from native to compiler/testData.

^KT-65979

compiler/testData/codegen/box/basics/unchecked_cast1.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+// JVM_ABI_K1_K2_DIFF: KT-63864
+// WITH_STDLIB
+import kotlin.test.*
+
+val sb = StringBuilder()
+
+fun box(): String {
+    foo<String>("17")
+    bar<String>("17")
+    foo<String>(42)
+    bar<String>(42)
+
+    assertEquals("17\n17\n42\n42\n", sb.toString())
+    return "OK"
+}
+
+fun <T> foo(x: Any?) {
+    val y = x as T
+    sb.appendLine(y.toString())
+}
+
+fun <T> bar(x: Any?) {
+    val y = x as? T
+    sb.appendLine(y.toString())
+}