ControllerInterface: devices population is now async so implement devices sorting priority

This helps us keeping the most important devices (e.g. Mouse and Keyboard) on the top
of the list of devices (they still are on all OSes supported by dolphin
and to make hotplug devices like DSU appear at the bottom.

Source/Core/InputCommon/ControllerInterface/CoreDevice.h

@@ -128,6 +128,11 @@ public:
   // (e.g. Xbox 360 controllers have controller number LEDs which should match the ID we use.)
   virtual std::optional<int> GetPreferredId() const;
 
+  // Use this to change the order in which devices are sorted in their list.
+  // A higher priority means it will be one of the first ones (smaller index), making it more
+  // likely to be index 0, which is automatically set as the default device when there isn't one.
+  virtual int GetSortPriority() const { return 0; }
+
   const std::vector<Input*>& Inputs() const { return m_inputs; }
   const std::vector<Output*>& Outputs() const { return m_outputs; }