[C++] fix STL header includes for NodeImpl.cc and Stream.cc (#3471)

MSVC complains about missing symbols:

```
lang/c++/impl/Stream.cc(183): error C2039: 'back_inserter': is not a member of 'std'
lang/c++/impl/Stream.cc(183): error C3861: 'back_inserter': identifier not found
```

Signed-off-by: Stephan Lachnit <stephanlachnit@debian.org>

Author: stephanlachnit

lang/c++/impl/NodeImpl.cc

@@ -17,8 +17,13 @@
  */
 
 #include "NodeImpl.hh"
-#include <sstream>
+
+#include <cctype>
+#include <locale>
+#include <ostream>
+#include <string>
 #include <utility>
+#include <vector>
 
 using std::string;
 namespace avro {

lang/c++/impl/Stream.cc

@@ -17,6 +17,10 @@
  */
 
 #include "Stream.hh"
+
+#include <algorithm>
+#include <iterator>
+#include <memory>
 #include <vector>
 
 namespace avro {