fix: make_filter_cmd for :! powershell #15913

Problem:
Nvim fails to create tempfile "…/nvim6UJx04/7" when 'shell' is set to
pwsh (PowerShell Core). This breaks filtered shell commands ":{range}!".
With shell set to cmd, it works.

Solution:
PowerShell doesn't use "<" for stdin redirection. Instead, use
"-RedirectStandardInput".

Closes #15913

test/functional/helpers.lua

@@ -525,9 +525,9 @@ function module.set_shell_powershell()
   module.exec([[
     let &shell = ']]..shell..[['
     set shellquote= shellxquote=
-    let &shellpipe = '2>&1 | Out-File -Encoding UTF8 %s; exit $LastExitCode'
-    let &shellredir = '2>&1 | Out-File -Encoding UTF8 %s; exit $LastExitCode'
     let &shellcmdflag = '-NoLogo -NoProfile -ExecutionPolicy RemoteSigned -Command ]]..cmd..[['
+    let &shellpipe = '2>&1 | Out-File -Encoding UTF8 %s; exit $LastExitCode'
+    let &shellredir = '-RedirectStandardOutput %s -NoNewWindow -Wait'
   ]])
 end