popn: boot with 3 monitors (#636)

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

## Description of change
Take the monitor hooks added for IIDX/SDVX #612 and apply it to popn as
well now that popn has a subscreen.

There is a debug option in game that actually uses three monitors, which
can be activated via hex edits. This will prevent that from working.

## Testing
Tested with 3 monitors, fs and windowed.

src/spice2x/launcher/options.cpp

@@ -997,6 +997,17 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .game_name = "Pop'n Music",
         .category = "Game Options",
     },
+    {
+        // PopnSubMonitorOverride
+        .title = "Pop'n Music PikaPika Subscreen Monitor Override",
+        .name = "popnsubmonitor",
+        .desc = "If you have three or more monitors, this option can be set to tell the game which monitor is the subscreen.",
+        .type = OptionType::Text,
+        .setting_name = "\\\\.\\DISPLAY3",
+        .game_name = "Pop'n Music",
+        .category = "Monitor",
+        .picker = OptionPickerType::Monitor,
+    },
     {
         .title = "Force Load HELLO! Pop'n Music Module",
         .name = "hpm",