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

^KT-65979

compiler/testData/codegen/box/basics/unchecked_cast2.kt

@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+// KT-66086
+// IGNORE_BACKEND: NATIVE
+// KT-66084
+// IGNORE_BACKEND: JS_IR, JS_IR_ES6
+// KT-66085
+// IGNORE_BACKEND: WASM
+// WITH_STDLIB
+import kotlin.test.*
+
+fun box(): String {
+    try {
+        val x = cast<String>(Any())
+        return "FAIL: ${x.length}"
+    } catch (e: Throwable) {
+        return "OK"
+    }
+}
+
+fun <T> cast(x: Any?) = x as T