Add on_load to AsyncImage (#5195)
Add on_load to AsyncImage (#5195)

* Add on_complete to AsyncImage

* Use existing on_load

* Force dispatch

if bound to ProxyImage.on_load, it won't get triggered after the texture is loaded

LogicalDash/kivy,inclement/kivy,rnixx/kivy,bionoid/kivy,Cheaterman/kivy,rnixx/kivy,jkankiewicz/kivy,jkankiewicz/kivy,jkankiewicz/kivy,manthansharma/kivy,manthansharma/kivy,manthansharma/kivy,Cheaterman/kivy,manthansharma/kivy,akshayaurora/kivy,matham/kivy,rnixx/kivy,Cheaterman/kivy,LogicalDash/kivy,janssen/kivy,LogicalDash/kivy,jegger/kivy,bionoid/kivy,kivy/kivy,jegger/kivy,LogicalDash/kivy,matham/kivy,KeyWeeUsr/kivy,matham/kivy,janssen/kivy,jegger/kivy,Cheaterman/kivy,janssen/kivy,KeyWeeUsr/kivy,bionoid/kivy,inclement/kivy,bionoid/kivy,akshayaurora/kivy,kivy/kivy,jkankiewicz/kivy,KeyWeeUsr/kivy,KeyWeeUsr/kivy,janssen/kivy,inclement/kivy,kivy/kivy,jegger/kivy,matham/kivy,akshayaurora/kivy