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/core/cheats/gateway_cheat.h

@@ -0,0 +1,83 @@
+// Copyright 2018 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <atomic>
+#include <memory>
+#include "core/cheats/cheat_base.h"
+
+namespace Cheats {
+class GatewayCheat final : public CheatBase {
+public:
+    enum class CheatType {
+        Null = -0x1,
+        Write32 = 0x00,
+        Write16 = 0x01,
+        Write8 = 0x02,
+        GreaterThan32 = 0x03,
+        LessThan32 = 0x04,
+        EqualTo32 = 0x05,
+        NotEqualTo32 = 0x06,
+        GreaterThan16WithMask = 0x07,
+        LessThan16WithMask = 0x08,
+        EqualTo16WithMask = 0x09,
+        NotEqualTo16WithMask = 0x0A,
+        LoadOffset = 0x0B,
+        Loop = 0x0C,
+        Terminator = 0xD0,
+        LoopExecuteVariant = 0xD1,
+        FullTerminator = 0xD2,
+        SetOffset = 0xD3,
+        AddValue = 0xD4,
+        SetValue = 0xD5,
+        IncrementiveWrite32 = 0xD6,
+        IncrementiveWrite16 = 0xD7,
+        IncrementiveWrite8 = 0xD8,
+        Load32 = 0xD9,
+        Load16 = 0xDA,
+        Load8 = 0xDB,
+        AddOffset = 0xDC,
+        Joker = 0xDD,
+        Patch = 0xE,
+    };
+
+    struct CheatLine {
+        explicit CheatLine(const std::string& line);
+        CheatType type;
+        u32 address;
+        u32 value;
+        u32 first;
+        std::string cheat_line;
+    };
+
+    GatewayCheat(std::string name, std::vector<CheatLine> cheat_lines, std::string comments);
+    ~GatewayCheat();
+
+    void Execute(Core::System& system) override;
+
+    bool IsEnabled() const override;
+    void SetEnabled(bool enabled) override;
+
+    std::string GetComments() const override;
+    std::string GetName() const override;
+    std::string GetType() const override;
+    std::string ToString() const override;
+
+    /// Gateway cheats look like:
+    ///     [Name]
+    ///     12345678 90ABCDEF
+    ///     12345678 90ABCDEF
+    ///     (there might be multiple lines of those hex numbers)
+    ///     Comment lines start with a '*'
+    /// This function will pares the file for such structures
+    static std::vector<std::unique_ptr<CheatBase>> LoadFile(const std::string& filepath);
+
+private:
+    std::atomic<bool> enabled = false;
+    const std::string name;
+    const std::vector<CheatLine> cheat_lines;
+    const std::string comments;
+};
+} // namespace Cheats