move a bunch of migration-dependent stuff from PsiPackageImpl.processDeclarations() toi MigrationElementFinder

java/java-psi-api/src/com/intellij/psi/PsiElementFinder.java

@@ -81,7 +81,7 @@ public abstract class PsiElementFinder {
    */
   @NotNull
   public PsiPackage[] getSubPackages(@NotNull PsiPackage psiPackage, @NotNull GlobalSearchScope scope) {
-    return new PsiPackage[0];
+    return PsiPackage.EMPTY_ARRAY;
   }
 
   /**

java/java-psi-api/src/com/intellij/psi/PsiPackage.java

@@ -26,6 +26,8 @@ import org.jetbrains.annotations.Nullable;
  * Represents a Java package.
  */
 public interface PsiPackage extends PsiCheckedRenameElement, NavigationItem, PsiModifierListOwner, PsiDirectoryContainer, PsiQualifiedNamedElement {
+  PsiPackage[] EMPTY_ARRAY = new PsiPackage[0];
+
   /**
    * Returns the full-qualified name of the package.
    *