Dropping package facades:

- light classes: do not generate light class for package facade
- drop package facades as multifile classes compilation mode support
- get rid of some additional package facade fqName usages
- update tests for light classes

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/PackageClassUtils.java

@@ -31,7 +31,7 @@ public final class PackageClassUtils {
 
     // ex. <root> -> _DefaultPackage, a -> APackage, a.b -> BPackage
     @NotNull
-    public static String getPackageClassName(@NotNull FqName packageFQN) {
+    private static String getPackageClassName(@NotNull FqName packageFQN) {
         if (packageFQN.isRoot()) {
             return DEFAULT_PACKAGE_CLASS_NAME;
         }