popn: subscreen overlay (#631)

## Link to GitHub Issue or related Pull Request, if one exists
#618 

## Description of change

Add overlay for subscreen.

Add an option for no subscreen window.

Use the same "force redraw subscreen" logic we used in SDVX to fix the
same issue.

Known issues:

* still crashing when running windowed if there is only one monitor
* having only one monitor causes sunscreen overlay to not work
(NumberOfAdaptersInGroup issue?)

## Testing

src/spice2x/games/popn/popn.h

@@ -6,9 +6,17 @@
 namespace games::popn {
 
     static inline bool is_pikapika_model() {
+
+#if SPICE64
         return (avs::game::is_model("M39") && avs::game::SPEC[0] == 'D');
+#else
+        return false;
+#endif
+
     }
 
+    extern bool SHOW_PIKA_MONITOR_WARNING;
+
     class POPNGame : public games::Game {
     public:
         POPNGame();