VideoCommon/NetPlayChatUI: Take std::string by value in AppendChat()

Given we're simply storing the std::string into a deque. We can emplace
it and move it. Completely avoiding copies with the current usage of the
function.

Source/Core/VideoCommon/NetPlayChatUI.cpp

@@ -78,12 +78,12 @@ void NetPlayChatUI::Display()
   ImGui::End();
 }
 
-void NetPlayChatUI::AppendChat(const std::string& message, NetPlayChatUI::Color color)
+void NetPlayChatUI::AppendChat(std::string message, Color color)
 {
   if (m_messages.size() > MAX_BACKLOG_SIZE)
     m_messages.pop_front();
 
-  m_messages.push_back({message, color});
+  m_messages.emplace_back(std::move(message), color);
 
   // Only scroll to bottom, if we were at the bottom previously
   if (m_is_scrolled_to_bottom)

Source/Core/VideoCommon/NetPlayChatUI.h

@@ -20,7 +20,7 @@ public:
   using Color = std::array<float, 3>;
 
   void Display();
-  void AppendChat(const std::string& message, Color color);
+  void AppendChat(std::string message, Color color);
   void SendMessage();
   void Activate();