Add function exec-suffixes

Add function exec-suffixes

* doc/lispref/processes.texi (Subprocess Creation):
Add function exec-suffixes.

* etc/NEWS: New function 'exec-suffixes'.
Presentational fixes and improvements.

* lisp/files-x.el (exec-suffixes): New defun.  (Bug#78886)

* lisp/files.el (executable-find): Use function `exec-suffixes'.

* lisp/net/tramp-integration.el
(tramp-connection-local-default-system-variables): Add also
`exec-suffixes'.

* lisp/net/tramp-smb.el (tramp-smb-maybe-open-connection): Use
default values of `path-separator', `null-device' and
`exec-suffixes'.
(tramp-smb-connection-local-default-system-variables):
New defconst.  Add it to connection-local profiles.

(cherry picked from commit 5a7a12d7920a94edea175871235c5013f0c73e3c)