AAPT2: propagate SPEC_OVERLAYABLE to splits

A resource marked SPEC_OVERLAYABLE in the base package was not marked as
such in the corresponding split packages. Add missing copy statement.

Test: manual (aapt2 dump test content in libandroidfw)
Change-Id: I800e92111a9da7c6f5e83f8a546d260c8d93b308
(cherry picked from commit ee41b3a36dcd87f79f3c2a21383a97743530099d)
diff --git a/tools/aapt2/split/TableSplitter.cpp b/tools/aapt2/split/TableSplitter.cpp
index 414758e..2e717ff 100644
--- a/tools/aapt2/split/TableSplitter.cpp
+++ b/tools/aapt2/split/TableSplitter.cpp
@@ -248,6 +248,7 @@
             if (!split_entry->id) {
               split_entry->id = entry->id;
               split_entry->visibility = entry->visibility;
+              split_entry->overlayable_declarations = entry->overlayable_declarations;
             }
 
             // Copy the selected values into the new Split Entry.