PR Summary

This PR replaces all occurrences of PsUtils.GetMainModule(currentProcess).FileName with the new Environment.ProcessPath API as suggested in #14332 (comment).
Furthermore, all the other places in which a ProcessModule needs to be retrieved have been changed to use Process.MainModule .NET API directly instead of going through PSUtils.GetMainModule (which has been removed).

PR Context

In the comment linked above, Ilya (@iSazonov) reported that calling PsUtils.GetMainModule(currentProcess).FileName was particularly expensive (27ms). The new Environment.ProcessPath API has been implemented to tackle this problem and there is even an official .NET analyzer to recommend switching to it (dotnet/roslyn-analyzers#4909).
While making that change, I noticed that PSUtils.GetMainModule wrapped Process.MainModule in a retry loop to workaround a .NET Framework 2.0 (!) BCL issue, therefore it shouldn't be needed at all nowadays.

Fixes #13790

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