Cache of the last Sprite added to sprites_to_update since the last call to draw

Property definitions

gamnit $ SpriteContext :: last_sprite_to_update=
	# Cache of the last `Sprite` added to `sprites_to_update` since the last call to `draw`
	var last_sprite_to_update: nullable Sprite = null
lib/gamnit/flat/flat_core.nit:1066,2--1067,50