Add a typeName() method to each type for error printing purposes.

Test: compiles with mma
Change-Id: I1283c395440282fde1106ad47aa185bdeda75880
diff --git a/Interface.h b/Interface.h
index 02b04dc..a786ce3 100644
--- a/Interface.h
+++ b/Interface.h
@@ -35,6 +35,7 @@
     bool isBinder() const override;
     bool isRootType() const { return mSuperType == nullptr; }
     bool isIBase() const { return fqName() == gIBaseFqName; }
+    std::string typeName() const override;
 
     const Interface *superType() const;