rawinput: add basic support for xinput (#617)

## Link to GitHub Issue or related Pull Request, if one exists
#616 

## Description of change
Adds preliminary support for XInput controllers. Enough to manually bind
buttons and map analogs.

src/spice2x/rawinput/xinput.h

@@ -0,0 +1,94 @@
+#pragma once
+
+#include <cstdint>
+#include <array>
+#include <vector>
+#include <string>
+
+#include <windows.h>
+
+namespace xinput {
+
+    #define XUSER_MAX_COUNT 4
+
+    typedef struct _XINPUT_GAMEPAD_STATE {
+        uint16_t wButtons;
+        uint8_t bLeftTrigger;
+        uint8_t bRightTrigger;
+        int16_t sThumbLX;
+        int16_t sThumbLY;
+        int16_t sThumbRX;
+        int16_t sThumbRY;
+    } XINPUT_GAMEPAD_STATE;
+
+    typedef struct _XINPUT_GAMEPAD_STATE_NORMALIZED {
+        uint16_t wButtons;
+        float bLeftTrigger;
+        float bRightTrigger;
+        float sThumbLX;
+        float sThumbLY;
+        float sThumbRX;
+        float sThumbRY;
+    } XINPUT_GAMEPAD_STATE_NORMALIZED;
+
+    enum class XInputButtonEnum {
+        // actual buttons
+        DPAD_UP,
+        DPAD_DOWN,
+        DPAD_LEFT,
+        DPAD_RIGHT,
+        START,
+        BACK,
+        LEFT_STICK,
+        RIGHT_STICK,
+        LEFT_SHOULDER,
+        RIGHT_SHOULDER,
+        BUTTON_A,
+        BUTTON_B,
+        BUTTON_X,
+        BUTTON_Y,
+
+        // analog values that can be used as buttons
+        LEFT_TRIGGER,
+        RIGHT_TRIGGER,
+        LEFT_STICK_UP,
+        LEFT_STICK_DOWN,
+        LEFT_STICK_LEFT,
+        LEFT_STICK_RIGHT,
+        RIGHT_STICK_UP,
+        RIGHT_STICK_DOWN,
+        RIGHT_STICK_LEFT,
+        RIGHT_STICK_RIGHT,
+
+        COUNT
+    };
+
+    enum class XInputAnalogEnum {
+        // analog values
+        LEFT_TRIGGER,
+        RIGHT_TRIGGER,
+        LEFT_STICK_X,
+        LEFT_STICK_Y,
+        RIGHT_STICK_X,
+        RIGHT_STICK_Y,
+
+        COUNT
+    };
+
+    std::string get_button_string(XInputButtonEnum button);
+    std::string get_analog_string(XInputAnalogEnum analog);
+
+    class XInputManager {
+    private:
+        bool initialized = false;
+        HMODULE xinput_lib = nullptr;
+        void get_state(uint8_t player, XINPUT_GAMEPAD_STATE_NORMALIZED *state);
+    public:
+        XInputManager();
+        ~XInputManager();
+        void stop();
+        std::vector<uint8_t> get_available_players();
+        bool is_button_pressed(uint8_t player, XInputButtonEnum button);
+        float get_analog_state(uint8_t player, XInputAnalogEnum analog);
+    };
+}