gitadora: (arena model) booting fullscreen with one monitor (#696)

## Link to GitHub Issue or related Pull Request, if one exists
#477 

## Description of change
By default the game needs 4 monitors.

With the new option to disable subscreens, you can now boot fullscreen
with a single 4K monitor, with subscreen overlay enabled. Side monitors
are not shown in the overlay; only the touch screen is emulated.

## Future work

- [ ] custom resolution (-forceres) doesn't work properly (hooking
ResetEx does allow the game to boot but will render incorrectly;
probably needs hex edits)
- [x] enable this automatically if the user has fewer than 4 monitors
- [ ] ability to boot with a 4k main screen + small subscreen (with no
side screens which do nothing gameplay wise), but this whole display
emulation is a nightmare to work with & test thoroughly so it'll have to
be in the future.


## Testing
Checklist:

- [x] fs on 1 monitor with option set
- [x] fs on 2 monitor with option set
- [x] windowed - default (4 windows, no overlay)
- [x] windowed - with option set (1 window, overlay)
- [x] fs with 4 monitors?
- [x] check popn hc for regression

src/spice2x/launcher/launcher.cpp

@@ -644,8 +644,11 @@ int main_implementation(int argc, char *argv[]) {
     if (options[launcher::Options::GitaDoraCabinetType].is_active()) {
         games::gitadora::CAB_TYPE = options[launcher::Options::GitaDoraCabinetType].value_uint32();
     }
-    if (options[launcher::Options::GitaDoraArenaSingleWindow].value_bool() && GRAPHICS_WINDOWED) {
-        games::gitadora::ARENA_SINGLE_WINDOW = true;
+    if (options[launcher::Options::GitaDoraArenaSingleWindow].value_bool()) {
+        // for full screen
+        GRAPHICS_FORCE_SINGLE_ADAPTER = true;
+        // for windowed
+        GRAPHICS_PREVENT_SECONDARY_WINDOW = true;
     }
     if (options[launcher::Options::GitaDoraWailHold].is_active()) {
         socd::TILT_HOLD_MS = options[launcher::Options::GitaDoraWailHold].value_uint32();