patch 8.2.2669: command line completion does not work after "vim9"

Problem:    Command line completion does not work after "vim9".
Solution:   Include the "9". (Naohiro Ono, closes #8025)

src/cmdexpand.c

@@ -1020,8 +1020,9 @@ set_one_cmd_context(
 	p = cmd;
 	while (ASCII_ISALPHA(*p) || *p == '*')    // Allow * wild card
 	    ++p;
-	// a user command may contain digits
-	if (ASCII_ISUPPER(cmd[0]))
+	// A user command may contain digits.
+	// Include "9" for "vim9*" commands; "vim9cmd" and "vim9script".
+	if (ASCII_ISUPPER(cmd[0]) || STRNCMP("vim9", cmd, 4) == 0)
 	    while (ASCII_ISALNUM(*p) || *p == '*')
 		++p;
 	// for python 3.x: ":py3*" commands completion

src/ex_docmd.c

@@ -3553,7 +3553,7 @@ find_ex_command(
 	}
 	else if (*p == '9' && STRNCMP("vim9", eap->cmd, 4) == 0)
 	{
-	    // include "9" for "vim9script"
+	    // include "9" for "vim9*" commands; "vim9cmd" and "vim9script".
 	    ++p;
 	    while (ASCII_ISALPHA(*p))
 		++p;

src/testdir/test_cmdline.vim

@@ -871,6 +871,10 @@ func Test_cmdline_complete_various()
   call feedkeys(":py3\<C-A>\<C-B>\"\<CR>", 'xt')
   call assert_equal('"py3 py3do py3file', @:)
 
+  " completion for the :vim9 commands
+  call feedkeys(":vim9\<C-A>\<C-B>\"\<CR>", 'xt')
+  call assert_equal('"vim9cmd vim9script', @:)
+
   " redir @" is not the start of a comment. So complete after that
   call feedkeys(":redir @\" | cwin\t\<C-B>\"\<CR>", 'xt')
   call assert_equal('"redir @" | cwindow', @:)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2669,
 /**/
     2668,
 /**/