Add a doc about encoding configuration

[rjmholt]

PR Summary

Adds a document that deals with configuring encoding in VSCode and PowerShell so that there are no nasty surprises.

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[TylerLeonhardt]

This should go on PowerShell-Docs instead I think. Can you move it there before we get too many comments?

[rkeithhill]

Does this apply to both Windows PowerShell and PowerShell Core? I thought PowerShell Core was immune from this issue? If so, maybe this should say "Windows PowerShell"? OK, it appears that pwsh on Windows doesn't use utf-8 (no BOM). But pwsh on Linux, and presumably macOS, do use utf-8. So maybe this should be "to prevent encoding bugs on Windows"?

[rkeithhill]

Nevermind, the above was clarified after reading the rest of the doc.

[rkeithhill]

It may be worth pointing out that you can make this encoding change just for PoweShell files:

    "[powershell]": {
        "files.encoding": "utf8bom"
    }

[rkeithhill]

Outstandind! Only one little comment on how to make the VSCode file encoding setting be specific to PowerShell files.

[TylerLeonhardt]

This doc brought tears to my eyes it was so good. LGTM. Just people move it to the other repo.