Qt/GCMemcardManager and Qt/GameCubePane: Give detailed error messages for invalid memory cards.

Source/Core/DolphinQt/GCMemcardManager.h

@@ -12,6 +12,7 @@
 #include <QDialog>
 
 class GCMemcard;
+class GCMemcardErrorCode;
 
 class QDialogButtonBox;
 class QGroupBox;
@@ -19,6 +20,7 @@ class QLabel;
 class QLineEdit;
 class QPixmap;
 class QPushButton;
+class QString;
 class QTableWidget;
 class QTimer;
 
@@ -29,6 +31,8 @@ public:
   explicit GCMemcardManager(QWidget* parent = nullptr);
   ~GCMemcardManager();
 
+  static QString GetErrorMessagesForErrorCode(const GCMemcardErrorCode& code);
+
 private:
   void CreateWidgets();
   void ConnectWidgets();