InputCommon: Fix callback dispatch deadlock

Make sure m_is_populating_devices is true when a WM_INPUT_DEVICE_CHANGE
event is received directly on the ciface thread, so that callbacks do
not occur while removing devices. This breaks a hold-and-wait deadlock
between the ciface thread and the CPU thread when using emulated
Wiimotes.

Co-authored-by: brainleq <brainleq@users.noreply.github.com>
Co-authored-by: oldmud0 <oldmud0@users.noreply.github.com>

Source/Core/InputCommon/ControllerInterface/ControllerInterface.h

@@ -50,6 +50,7 @@ public:
   void Shutdown();
   void AddDevice(std::shared_ptr<ciface::Core::Device> device);
   void RemoveDevice(std::function<bool(const ciface::Core::Device*)> callback);
+  void PlatformPopulateDevices(std::function<void()> callback);
   bool IsInit() const { return m_is_init; }
   void UpdateInput();