graphics: fix window resize not working properly in some games (#530)

## Link to GitHub Issue, if one exists
n/a

## Description of change
Need to filter out system-created windows (such as `CicMarshalWnd`) when
looking up which window to mess with when user interacts with F11 menu.

While I'm here, clean up the hack for gfdm arena model that remembers
the main window.

## Testing
Tested:

DDR
gfdm arena 4 / 1 window modes
iidx (windowed mode, with/without nosub option)
sdvx with sub windows

Need to check:
full screen games

src/spice2x/overlay/windows/screen_resize.cpp

@@ -27,11 +27,12 @@ namespace overlay::windows {
     }
 
     HWND ScreenResize::get_first_window() {
-        // hack for gitadora arena model which races to create many windows
-        // so [0] is not always the main one
-        if (GRAPHICS_WINDOW_MAIN.has_value()) {
-            return GRAPHICS_WINDOW_MAIN.value();
+        // this is ideal
+        if (GRAPHICS_HOOKED_WINDOW.has_value()) {
+            return GRAPHICS_HOOKED_WINDOW.value();
         }
+        // we typically do not want to check GRAPHICS_WINDOWS because it may include
+        // system windows (e.g., CicMarshalWnd)
         if (GRAPHICS_WINDOWS.size() == 0) {
             return NULL;
         }