[3006.x] Fix issues with the cmd module on Windows

[twangboy]

What does this PR do?

Fixes various issues with the cmd module on Windows:

• Piping stderr to stdout is not optional for cmd.run
• Scripts are called using the -Command & parameter for powershell.exe
• stderr is cleared if it contains CLIXML (only for encoded commands)
• cmd.powershell now accepts commands as lists
• Makes sure returned JSON data is valid before trying to load it
• Strips whitespace from the stdout in win_runas

What issues does this PR fix or reference?

Fixes #61166

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [x] Docs
• [x] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [x] Tests written/updated

Commits signed with GPG?

Yes