Refactor policy parsing

This change removes the ability for an overlayable resource to be
defined in multiple policy blocks within the same overlayable. This
change also changes aapt2 to use a bit mask to keep track of the parsed
policies.

Bug: 110869880
Bug: 120298168
Test: aapt2_tests
Change-Id: Ie26cd913f94a16c0b312f222bccfa48f62feceaa
diff --git a/tools/aapt2/link/ReferenceLinker.cpp b/tools/aapt2/link/ReferenceLinker.cpp
index 1b6626a..8cbc037 100644
--- a/tools/aapt2/link/ReferenceLinker.cpp
+++ b/tools/aapt2/link/ReferenceLinker.cpp
@@ -374,8 +374,8 @@
         }
 
         // Ensure that definitions for values declared as overlayable exist
-        if (!entry->overlayable_declarations.empty() && entry->values.empty()) {
-          context->GetDiagnostics()->Error(DiagMessage(entry->overlayable_declarations[0].source)
+        if (entry->overlayable && entry->values.empty()) {
+          context->GetDiagnostics()->Error(DiagMessage(entry->overlayable.value().source)
                                            << "no definition for overlayable symbol '"
                                            << name << "'");
           error = true;