support CreateProcessAsUserA in windows for Command module

[RickSKy]

Is your feature request related to a problem? Please describe. tokio::process::Command may need use another user to run in some cases.

Describe the solution you'd like add an function to set the token for CreateProcessAsUserA like creation_flags() in windows platform

[Darksonn]

Thoughts? @ipetkov

[ipetkov]

Looks like there is an extension trait in the standard library which allows for setting arbitrary creation_flags()

We can easily add the same API but I think that won't help since the process needs to be created with CreateProcessAsUserW while the standard library uses CreateProcessW

[notgull]

Could this be added to the standard library? This could be useful for non-async usage as well

[Darksonn]

Tokio currently works by using the implementation in the standard library, so if std doesn't support it, then supporting it in Tokio without first supporting it in std would require a complete rewrite of tokio::process. I don't think that would be worth it.