rawinput: fix hotplug for keyboard and mouse (#810)

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

## Description of change
Fix a long-standing issue of hotplug not working for keyboards and mice.
The code only registered for HID notifications; we also need to do it
for the keyboard GUID and mouse GUID.

## Testing
Confirmed that keyboards and mice can be hot unplugged and plugged.

src/spice2x/rawinput/hotplug.h

@@ -9,7 +9,9 @@ namespace rawinput {
     class HotplugManager {
     private:
         RawInputManager *ri_mgr;
-        HANDLE hotplug_hid;
+        HANDLE hotplug_hid = nullptr;
+        HANDLE hotplug_keyboard = nullptr;
+        HANDLE hotplug_mouse = nullptr;
 
     public:
         HotplugManager(RawInputManager *ri_mgr, HWND hwnd);