patch 9.1.1166: command-line auto-completion hard with wildmenu

Problem:  command-line auto-completion hard with wildmenu
Solution: implement "noselect" wildoption value (Girish Palya)

When `noselect` is present in `wildmode` and 'wildmenu' is enabled, the
completion menu appears without pre-selecting the first item.

This change makes it easier to implement command-line auto-completion,
where the menu dynamically appears as characters are typed, and `<Tab>`
can be used to manually select an item. This can be achieved by
leveraging the `CmdlineChanged` event to insert `wildchar(m)`,
triggering completion menu.

Without this change, auto-completion using the 'wildmenu' mechanism is
not feasible, as it automatically inserts the first match, preventing
dynamic selection.

The following Vimscript snippet demonstrates how to configure
auto-completion using `noselect`:

```vim
vim9script
set wim=noselect:lastused,full wop=pum wcm=<C-@> wmnu
autocmd CmdlineChanged : timer_start(0, function(CmdComplete, [getcmdline()]))

def CmdComplete(cur_cmdline: string, timer: number)
  var [cmdline, curpos] = [getcmdline(), getcmdpos()]
  if cur_cmdline ==# cmdline  # Avoid completing each character in keymaps and pasted text
    && !pumvisible() && curpos == cmdline->len() + 1

    if cmdline[curpos - 2] =~ '[\w*/:]'  # Reduce noise by completing only selected characters
      feedkeys("\<C-@>", "ti")
      set eventignore+=CmdlineChanged  # Suppress redundant completion attempts
      timer_start(0, (_) => {
        getcmdline()->substitute('\%x00$', '', '')->setcmdline()  # Remove <C-@> if no completion items exist
        set eventignore-=CmdlineChanged
      })
    endif
  endif
enddef
```

fixes: #16551
closes: #16759

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/cmdexpand.c b/src/cmdexpand.c
index 9f24429..597f78d 100644
--- a/src/cmdexpand.c
+++ b/src/cmdexpand.c
@@ -286,6 +286,9 @@
 	{
 	    int use_options = options |
 		    WILD_HOME_REPLACE|WILD_ADD_SLASH|WILD_SILENT;
+	    if (use_options & WILD_KEEP_SOLE_ITEM)
+		use_options &= ~WILD_KEEP_SOLE_ITEM;
+
 	    if (escape)
 		use_options |= WILD_ESCAPE;
 
@@ -340,7 +343,7 @@
 
     if (xp->xp_numfiles <= 0 && p2 == NULL)
 	beep_flush();
-    else if (xp->xp_numfiles == 1)
+    else if (xp->xp_numfiles == 1 && !(options & WILD_KEEP_SOLE_ITEM))
 	// free expanded pattern
 	(void)ExpandOne(xp, NULL, NULL, 0, WILD_FREE);