feat(hitbox): add a way to advertise an hitbox as main hitbox

gamecore/modules/world/actors/actor2D.lua

@@ -243,6 +243,7 @@ end
 
 function Actor2D:initMainHitbox()
   self.mainHitbox = Hitbox(self, self.type, 0, 0, self.w, self.h, self.isSolid)
+  self.mainHitbox:advertiseAsMainHitbox()
 end
 
 function Actor2D:addHitbox(name, type, ox, oy, w, h, isSolid)

gamecore/modules/world/actors/utils/hitbox2D.lua

@@ -39,10 +39,16 @@ function Hitbox2D:new(owner, type, ox, oy, w, h, isSolid)
   self.h        = h
   self.isSolid  = isSolid
 
+  self.isMainHitBox = false
+
   self:setDebugColor(0,0,0)
   self:register()
 end
 
+function Hitbox2D:advertiseAsMainHitbox()
+  self.isMainHitBox = true
+end
+
 function Hitbox2D:modify(ox, oy, w, h)
   self.ox       = ox
   self.oy       = oy