Add CheatEngine and support for Gateway cheats (#4406)

* Add CheatEngine; Add support for Gateway cheats; Add Cheat UI

* fix a potential crash on some systems

* fix substr with negative length

* Add Joker to the NonOp comp handling

* Fixup JokerOp

* minor fixup in patchop; add todo for nested loops

* Add comment for PadState member variable in HID

* fix: stol to stoul in parsing cheat file

* fix misplaced parsing of values; fix patchop code

* add missing break

* Make read_func and write_func a template parameter

src/citra_qt/cheats.h

@@ -0,0 +1,30 @@
+// Copyright 2018 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <QDialog>
+
+namespace Ui {
+class CheatDialog;
+} // namespace Ui
+
+class CheatDialog : public QDialog {
+    Q_OBJECT
+
+public:
+    explicit CheatDialog(QWidget* parent = nullptr);
+    ~CheatDialog();
+
+private:
+    std::unique_ptr<Ui::CheatDialog> ui;
+
+    void LoadCheats();
+
+private slots:
+    void OnCancel();
+    void OnRowSelected(int row, int column);
+    void OnCheckChanged(int state);
+};