vim-patch:9.1.0774: "shellcmdline" doesn't work with getcompletion() (#30750)

Problem:  "shellcmdline" doesn't work with getcompletion().
Solution: Use set_context_for_wildcard_arg() (zeertzjq).

closes: vim/vim#15834

85f36d61e0

src/nvim/eval.lua

@@ -3775,6 +3775,7 @@ M.funcs = {
       runtime		|:runtime| completion
       scriptnames	sourced script names |:scriptnames|
       shellcmd	Shell command
+      shellcmdline	Shell command line with filename arguments
       sign		|:sign| suboptions
       syntax		syntax file names |'syntax'|
       syntime		|:syntime| suboptions