Support dired-movement-style in dired-next-dirline and dired-prev-dirline

Support dired-movement-style in dired-next-dirline and dired-prev-dirline

* lisp/dired.el (dired-movement-style): Mention dired-next-dirline
and dired-prev-dirline in the docstring (bug#67303).
(dired-next-line): Refactor most code to dired--move-to-next-line.
(dired--move-to-next-line): New function with code from dired-next-line.
(dired--trivial-next-dirline): Rename from dired-next-dirline.
(dired-next-dirline): New function body that uses dired-movement-style,
dired--move-to-next-line and dired--trivial-next-dirline.
(dired-prev-dirline): Mention dired-movement-style in the docstring.