force Windows to always use preamble-free UTF8 input encoding (#22934)

* fixes #15770
* When running under the UTF-8 codepage, Powershell subprocesses will fail (eg, Start-Job, others) if the input encoding is using the default BOM preamble. This fix forces it to use no preamble in leaf_exec and win_shell, and includes tests to verify that Start-Job works.

lib/ansible/modules/windows/win_shell.ps1

@@ -90,6 +90,9 @@ $exec_args = $null
 If(-not $executable -or $executable -eq "powershell") {
     $exec_application = "powershell"
 
+    # force input encoding to preamble-free UTF8 so PS sub-processes (eg, Start-Job) don't blow up
+    $raw_command_line = "[Console]::InputEncoding = New-Object Text.UTF8Encoding `$false; " + $raw_command_line
+
     # Base64 encode the command so we don't have to worry about the various levels of escaping
     $encoded_command = [Convert]::ToBase64String([System.Text.Encoding]::Unicode.GetBytes($raw_command_line))