Re-enable adding intern table to image

Changed intern table to have a stack of tables similarily to
ClassTable. Adding an image intern table adds to the front of the
intern table stack. Also some cleanup.

Bug: 26317072

Change-Id: I7bbf9485b5dbbbf3707fed21e29de3beccfb8705
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 7f67ae4..7b32c5b 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -2333,7 +2333,7 @@
   if (HasZygoteSpace()) {
     return;
   }
-  Runtime::Current()->GetInternTable()->SwapPostZygoteWithPreZygote();
+  Runtime::Current()->GetInternTable()->AddNewTable();
   Runtime::Current()->GetClassLinker()->MoveClassTableToPreZygote();
   VLOG(heap) << "Starting PreZygoteFork";
   // Trim the pages at the end of the non moving space.