runtime(vim): Update base syntax, contain user command replacement text

Ensure that :command replacement text terminates at the end of the
logical line.

Add :command to the generator exclusion list.

fixes: #18414 (@Dougaak)
fixes: #18448 (Maxim Kim)
closes: #18415

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/vim.vim

@@ -919,6 +919,7 @@ syn region	vimUserCmdReplacement contained
       \ skip=+\n\s*\%(\\\|["#]\\ \)+
       \ end="$"
       \ contains=@vimContinue,@vimUserCmdList,vimComFilter
+      \ keepend
 syn region	vimUserCmdBlock	    contained
       \ matchgroup=vimSep
       \ start="{"