overlay: create a dedicated thread for polling hotkeys (#864)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Create a new thread that polls for the following hotkeys:

* super exit (both alt+f4 and bound key)
* coin insert
* screenshot

The goal is to make the capture of these more reliable, because before
this PR it wasn't.

## Testing

src/spice2x/rawinput/rawinput.cpp

@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <chrono>
 #include <cstdarg>
+#include <iterator>
 #include <map>
 #include <thread>
 #include <utility>
@@ -2543,6 +2544,30 @@ rawinput::Device *rawinput::RawInputManager::devices_get(const std::string &name
     return nullptr;
 }
 
+bool rawinput::RawInputManager::keyboard_combo_pressed(uint16_t first, uint16_t second) {
+    if (first >= 256 || second >= 256) {
+        return false;
+    }
+
+    std::lock_guard<std::recursive_mutex> devices_lock(this->devices_mutex);
+    for (auto &device : this->devices) {
+        if (device.type != rawinput::KEYBOARD ||
+            device.keyboardInfo == nullptr ||
+            device.mutex == nullptr) {
+            continue;
+        }
+
+        std::lock_guard<std::mutex> device_lock(*device.mutex);
+        const auto &states = device.keyboardInfo->key_states;
+        for (size_t page = 0; page < std::size(states); page += 256) {
+            if (states[page + first] && states[page + second]) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
 void rawinput::RawInputManager::add_callback_add(void *data, std::function<void (void *, Device *)> callback) {
     this->callback_add.push_back(DeviceCallback {
             .data = data,

src/spice2x/rawinput/rawinput.h

@@ -171,6 +171,7 @@ namespace rawinput {
 
         void __stdcall devices_print();
         Device *devices_get(const std::string &name, bool updated = false);
+        bool keyboard_combo_pressed(uint16_t first, uint16_t second);
 
         inline std::list<Device> &devices_get() {
             return devices;