Support non ascii commandline args

[hknielsen]

Using none ASCII chars for protoc on Windows are not handled well.
This adresses argument file at a location where either directory, or filename contains Unicode chars.

Specifically because MsBuild tool saves argument file in with the UserName appended to the .rsp file.
dotnet/msbuild#9232

But in general we should really handle if none ascii chars are in the path.

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[hknielsen]

@haberman im not sure how to fix the "unsafe fork" issue, do I need to do anything?

[fowles]

Instead of shifting the code to wchar's can we shift the environment to utf-8 as outlined in https://learn.microsoft.com/en-us/windows/apps/design/globalizing/use-utf8-code-page ?

[hknielsen]

@fowles thanks for the question! That let me on to this:
https://learn.microsoft.com/en-us/cpp/build/reference/utf-8-set-source-and-executable-character-sets-to-utf-8?view=msvc-170
I agree its much better than starting to go to wchar. Changed so we on windows compile with the /utf-8 flag