Allows features to link to other feature splits without namespacing.

Add uses-split dependencies to AppInfo. At link time, this is used
and allows features to reference other features, before
resource namespacing is implemented in Android Studio.

bug:135681292
Test: Link_test, ReferenceLinker_test, and integration tests.
Change-Id: Ifdf0067e7370552b6b9d4d6d4713d4484b6ea154
diff --git a/tools/aapt2/cmd/Diff.cpp b/tools/aapt2/cmd/Diff.cpp
index 262f4fc4e..d56994e 100644
--- a/tools/aapt2/cmd/Diff.cpp
+++ b/tools/aapt2/cmd/Diff.cpp
@@ -65,6 +65,12 @@
     return 0;
   }
 
+  const std::set<std::string>& GetSplitNameDependencies() override {
+    UNIMPLEMENTED(FATAL) << "Split Name Dependencies should not be necessary";
+    static std::set<std::string> empty;
+    return empty;
+  }
+
  private:
   std::string empty_;
   StdErrDiagnostics diagnostics_;