Get rid of duplicated #include code.

This is in preparation to add a new target for IServiceManagerDupe and
is also general cleanup.

Test: hidl_test
Bug: 32313592
Change-Id: I9427a042e1ef0b5432e227522b616a8a948f2acf
diff --git a/AST.h b/AST.h
index 50f69b3..9a3670c 100644
--- a/AST.h
+++ b/AST.h
@@ -146,6 +146,11 @@
     void getPackageAndVersionComponents(
             std::vector<std::string> *components, bool cpp_compatible) const;
 
+    static void generateCppPackageInclude(
+            Formatter &out,
+            const FQName &package,
+            const std::string &klass);
+
     std::string makeHeaderGuard(const std::string &baseName) const;
     void enterLeaveNamespace(Formatter &out, bool enter) const;