RRO: Added partition policies for overlays

<overlayable> tags can now have policy elements that indicate which
partition the overlay apk must reside on in order to be allowed to
overlay a resource. This change only adds parsing of <policy> and
encoding of policy in the proto ResourceTable. A later change will add
the encoding of policy and overlayable in the binary APK.

<overlayable>
  <policy type="system|vendor|product|product_services|public" >
    <item type="string" name="oof" />
  </policy>
</overlayable>

Bug: 110869880
Test: make aapt2_tests
Change-Id: I8d4ed7b0e01f981149c6e3190af1681073b79b03
diff --git a/tools/aapt2/test/Builders.cpp b/tools/aapt2/test/Builders.cpp
index f33ae31..03b59e0 100644
--- a/tools/aapt2/test/Builders.cpp
+++ b/tools/aapt2/test/Builders.cpp
@@ -135,6 +135,15 @@
   return *this;
 }
 
+ResourceTableBuilder& ResourceTableBuilder::AddOverlayable(const StringPiece& name,
+                                                           const Maybe<Overlayable::Policy> p) {
+  ResourceName res_name = ParseNameOrDie(name);
+  Overlayable overlayable;
+  overlayable.policy = p;
+  CHECK(table_->AddOverlayable(res_name, overlayable, GetDiagnostics()));
+  return *this;
+}
+
 StringPool* ResourceTableBuilder::string_pool() {
   return &table_->string_pool;
 }