kernel/server_session: Return a std::pair from CreateSessionPair()

Keeps the return type consistent with the function name. While we're at
it, we can also reduce the amount of boilerplate involved with handling
these by using structured bindings.

src/core/hle/kernel/server_session.h

@@ -6,6 +6,7 @@
 
 #include <memory>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "core/hle/kernel/object.h"
@@ -58,7 +59,7 @@ public:
         return parent.get();
     }
 
-    using SessionPair = std::tuple<SharedPtr<ServerSession>, SharedPtr<ClientSession>>;
+    using SessionPair = std::pair<SharedPtr<ServerSession>, SharedPtr<ClientSession>>;
 
     /**
      * Creates a pair of ServerSession and an associated ClientSession.