Restore positions reliably for abbreviated file names in saveplace.el

Restore positions reliably for abbreviated file names in saveplace.el

* lisp/saveplace.el (save-place-abbreviate-file-names): Add setter
function for rewriting `save-place-alist'.  Update docstring.
(save-place-to-alist): Save Abbreviated dired-filename.
(save-place-load-alist-from-file): Move this function above
`save-place-abbreviate-file-names' since it is used in the :set
function.
(save-place-find-file-hook):
(save-place-dired-hook): Use abbreviated file name when
`save-place-abbreviate-file-names' is non-nil.
(Bug#62413)