lfs: move the tracked file function creation to a method Once a commitable file format for tracked config is agreed upon, I can't see any reason to have a config based way to control this. (Other than convert. That will be necessary to override the file when converting to normal files. Also, converting to lfs needs this if not splicing the file in at the beginning. So maybe the existing config option should be `convert` specific.) Looking to hgeol for precedent, it looks like policy that affects how items are stored are handled only by the tracked file, while policy that affects the checkout can be handled by either a user config or the tracked file (but the latter takes precedence). We probably need a transition period, so this transition policy can be controlled by the function. Additionally, it provides a place for convert to wrap to override the file based config.