Merge #12683: Fix more constness violations in serialization code

172f5fa738 Support deserializing into temporaries (Pieter Wuille)
2761bca997 Merge READWRITEMANY into READWRITE (Pieter Wuille)

Pull request description:

  This is another fragment of improvements from #10785.

  The current serialization code does not support serializing/deserializing from/to temporaries (like `s >> CFlatData(script)`). As a result, there are many invocations of the `REF` macro which in addition to changing the reference type also changes the constness. This is unnecessary in C++11 as we can use rvalue references now instead.

  The first commit is an extra simplification we can make that removes the duplication of code between `READWRITE` and `READWRITEMANY` (and related functions).

Tree-SHA512: babfa9cb268cc3bc39917e4f0a90e4651c33d85032161e16547a07f3b257b7ca7940e0cbfd69f09439d26fafbb1a6cf6359101043407e2c7aeececf7f20b6eed

src/script/bitcoinconsensus.cpp

@@ -40,7 +40,7 @@ public:
     }
 
     template<typename T>
-    TxInputStream& operator>>(T& obj)
+    TxInputStream& operator>>(T&& obj)
     {
         ::Unserialize(*this, obj);
         return *this;