patch 8.2.2415: no way to check for the cmdwin feature

Problem:    No way to check for the cmdwin feature, cmdline_hist is now always
            enabled.
Solution:   Add has('cmdwin') support. Skip arglist test on Windows
            temporarily.
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index b1a2a9e..e59bd20 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -343,6 +343,8 @@
 endfunc
 
 func Test_compl_in_cmdwin()
+  CheckFeature cmdwin
+
   set wildmenu wildchar=<Tab>
   com! -nargs=1 -complete=command GetInput let input = <q-args>
   com! -buffer TestCommand echo 'TestCommand'