Merge from origin/emacs-27

3f610177ad Avoid sending systemd shutdown notifications if non-daemon
009df5cb3c * src/cmds.c (Fforward_line): Doc fix.  (Bug#46027)
ee1c54ebc0 Improve documentation of sendmail.el defcustom's

diff --cc lisp/mail/sendmail.el
Simple merge

diff --cc src/cmds.c
Simple merge

diff --cc src/emacs.c
Simple merge