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

^KT-65979

compiler/testData/codegen/box/dataflow/scope1.kt

@@ -0,0 +1,18 @@
+/*
+ * 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.
+ */
+// WITH_STDLIB
+
+import kotlin.test.*
+
+var b = true
+
+fun box(): String {
+    var x = 1
+    if (b) {
+        var x = 2
+    }
+    assertEquals(1, x)
+    return "OK"
+}

compiler/testData/codegen/box/dataflow/uninitialized_val.kt

@@ -0,0 +1,27 @@
+/*
+ * 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.
+ */
+// WITH_STDLIB
+
+import kotlin.test.*
+
+fun foo(b: Boolean): Int {
+    val x: Int
+    if (b) {
+        x = 1
+    } else {
+        x = 2
+    }
+
+    return x
+}
+
+fun box(): String {
+    val uninitializedUnused: Int
+
+    assertEquals(1, foo(true))
+    assertEquals(2, foo(false))
+
+    return "OK"
+}