vim-patch:9.0.0423: "for" and "while" not recognized after :vim9cmd and :legacy (#24825)

Problem:    "for" and "while" not recognized after :vim9cmd and :legacy.
            (Emanuele Torre)
Solution:   Recognize all the command modifiers. (closes vim/vim#11087)
            Add a test to check the list of modifiers.

9132426334

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/ex_docmd.c

@@ -2411,7 +2411,7 @@ int parse_command_modifiers(exarg_T *eap, const char **errormsg, cmdmod_T *cmod,
 
     char *p = skip_range(eap->cmd, NULL);
     switch (*p) {
-    // When adding an entry, also modify cmd_exists().
+    // When adding an entry, also modify cmdmods[]
     case 'a':
       if (!checkforcmd(&eap->cmd, "aboveleft", 3)) {
         break;
@@ -3051,6 +3051,7 @@ static struct cmdmod {
   { "confirm", 4, false },
   { "filter", 4, false },
   { "hide", 3, false },
+  { "horizontal", 3, false },
   { "keepalt", 5, false },
   { "keepjumps", 5, false },
   { "keepmarks", 3, false },