vim-patch:9.2.0425: Cannot silence undo/redo messages (#39554)

Problem:  Cannot silence undo/redo messages
Solution: Add "u" flag to 'shortmess' option
          (Shougo Matsushita).

fixes:  vim/vim#20049
closes: vim/vim#20107

d25f8d1b2c

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>

src/nvim/options.lua

@@ -8000,6 +8000,9 @@ local options = {
         	search count statistics.  The maximum limit can be set with
         	the 'maxsearchcount' option, see also |searchcount()|
         	function.
+          u	don't give undo and redo messages like			*shm-u*
+        	"1 line less; before #1  1 second ago", "Already at oldest
+        	change" or "Already at newest change"
 
         This gives you the opportunity to avoid that a change between buffers
         requires you to hit <Enter>, but still gives as useful a message as