transient-{set,save}-and-exit: New commands

Actually they are just aliases.  The separate entries
in `transient-predicate-map' is what makes the different.

These are intended for use in, e.g., `magit-diff-refresh'
and `magit-log-refresh', which use specialized classes whose
`transient-set-value' and `transient-save-value' additionally refresh
the buffer containing the diff/log.  I.e., there this commands serve
as variants of `magit-refresh', and all these commands are expected to
exit the transient.

Previously these transients instead bound `transient-set-value'
to "s" and `transient-save-value' to "w", and explicitly set their
`transient' slot to nil, but that was surprising because that also
causes the regular "C-x s" and "C-x C-s" bindings to behave that
way.

lisp/transient.el

@@ -1626,7 +1626,9 @@ of the corresponding object."
   "<transient-update>"            #'transient--do-stay
   "<transient-toggle-common>"     #'transient--do-stay
   "<transient-set>"               #'transient--do-call
+  "<transient-set-and-exit>"      #'transient--do-exit
   "<transient-save>"              #'transient--do-call
+  "<transient-save-and-exit>"     #'transient--do-exit
   "<transient-reset>"             #'transient--do-call
   "<describe-key-briefly>"        #'transient--do-stay
   "<describe-key>"                #'transient--do-stay
@@ -2655,15 +2657,21 @@ transient is active."
     (transient-undefined))))
 
 (defun transient-set ()
-  "Save the value of the active transient for this Emacs session."
+  "Set active transient's value for this Emacs session."
   (interactive)
   (transient-set-value (or transient--prefix transient-current-prefix)))
 
+(defalias 'transient-set-and-exit 'transient-set
+  "Set active transient's value for this Emacs session and exit.")
+
 (defun transient-save ()
-  "Save the value of the active transient persistenly across Emacs sessions."
+  "Save active transient's value for this and future Emacs sessions."
   (interactive)
   (transient-save-value (or transient--prefix transient-current-prefix)))
 
+(defalias 'transient-save-and-exit 'transient-save
+  "Save active transient's value for this and future Emacs sessions and exit.")
+
 (defun transient-reset ()
   "Clear the set and saved values of the active transient."
   (interactive)