[Enhancement] Allow Non-unique Character Selections (#638)

* Update PortMenu.cpp

* Update menus.c

src/menus.c

@@ -1547,8 +1547,11 @@ GLOBAL_ASM("asm/non_matchings/menus/main_menu_act.s")
  * hovered character at grid position `gridId`
  */
 bool is_character_spot_free(s32 gridId) {
-    s32 i;
-    for (i = 0; i < ARRAY_COUNT(gCharacterGridSelections); i++) {
+    if (CVarGetInteger("gUniqueCharacterSelections", true) == false) {
+        return true;
+    }
+  
+    for (size_t i = 0; i < ARRAY_COUNT(gCharacterGridSelections); i++) {
         if (gridId == gCharacterGridSelections[i]) {
             return false;
         }

src/port/ui/PortMenu.cpp

@@ -438,7 +438,13 @@ void PortMenu::AddRulesets() {
     // AddWidget(path, "Number of Laps", WIDGET_CVAR_SLIDER_INT)
     //     .CVar("gNumLaps")
     //     .Options(UIWidgets::IntSliderOptions().Min().Max(20).Step(1).DefaultValue(3));
-
+    AddWidget(path, "Unique Character Selections", WIDGET_CVAR_CHECKBOX)
+        .CVar("gUniqueCharacterSelections")
+        .Options(CheckboxOptions()
+          .Tooltip(
+            "Prevents players from selecting the same character")
+          .DefaultValue(true)
+        );
     AddWidget(path, "No Itemboxes", WIDGET_CVAR_CHECKBOX)
         .CVar("gDisableItemboxes")
         .Options(CheckboxOptions().Tooltip(