Severity: wishlist

Description:

Add new choices 'type and 'file to `bookmark-sort-flag'.  See [1].

Notes:

1) It feels strange to have value t meaning 'name and value nil meaning
'creation-time, but it's better to not change how things have been
working for many years.  A more flexible approach could offer a custom
function as a choice of `bookmark-sort-flag'.

2) I took the liberty to update some comments and docstrings, please
review.

3) I took the liberty to remove some code in `bookmark-bmenu-mode' that
seems to be unnecessary, please review.  Everything seems to be working
as expected according to my tests.  I can also write some tests.

4) Used `string-collate-lessp' in `bookmark-maybe-sort-alist' to match
`bookmark-bmenu--*-predicate' functions.

[1] https://lists.gnu.org/archive/html/emacs-devel/2022-11/msg00995.html