Initial internal member mangling

compiler/testData/codegen/boxWithStdlib/mangling/field.kt

@@ -0,0 +1,20 @@
+package test
+
+internal val noMangling = 1;
+
+class Z {
+    internal var noMangling = 1;
+}
+
+fun box(): String {
+    val clazz = Z::class.java
+    val classField = clazz.getDeclaredField("noMangling")
+    if (classField == null) return "Class internal backing field should exist"
+    if (!classField.isSynthetic) return "Class internal backing field should be synthetic"
+
+    val topLevel = Class.forName("test.FieldKt").getDeclaredField("noMangling")
+    if (topLevel == null) return "Top level internal backing field should exist"
+    if (!topLevel.isSynthetic) return "Top level internal backing field should be synthetic"
+
+    return "OK"
+}