Specify encoding of the bookmark file

Specify encoding of the bookmark file

* lisp/bookmark.el (bookmark-insert-file-format-version-stamp):
Accept an argument CODING and include a 'coding:' cookie in the
bookmark file preamble.
(bookmark-upgrade-file-format-from-0): Call
'bookmark-insert-file-format-version-stamp' with the file buffer's
encoding, as detected when it was read.
(bookmark-file-coding-system): New variable.
(bookmark-load): Set bookmark-file-coding-system to the encoding
of the loaded file.
(bookmark-write-file): Bind coding-system-for-write to either the
user setting via "C-x RET c" or to the existing file encoding,
defaulting to 'utf-8-emacs'.  Update the value of
bookmark-file-coding-system.  (Bug#25365)