Adds keywords for Powershell

[cgranleese-r7]

Fixes rapid7/metasploit-framework#20331.

Adds what I believe are the required keywords for Powershell to the generator.

I added sources for where I got everything from. I may have went overboard on what needs covered, but I thought I cover what I seen and can cut it back if needed.

Verification

• Verify this fix will avoid collisions (msfvenom psh-cmd payload's random powershell function name collides with builtin commands metasploit-framework#20331)
• Code changes are sane
• Forbidden list covers required keywords etc

[adfoster-r7]

You'll need another PR to update the code to specify the powershell language and to ensure you've updated this library version dependency too 👍