Update HttpRequest Clone Method

[peombwa]

Fixes #2064 by addressing thread safety intermittent bug in .NET framework when copying request content header.

Changes proposed in this pull request

• Updates how request content headers are copied when cloning a request.

[jberezanski-mdg]

I'm not sure this will fix the problem. The update from

 foreach (var contentHeader in originalRequest.Content.Headers)

to

originalRequest.Content.Headers?.ToList()

does not change the behavior much - ToList() still iterates the Dictionary contained inside HttpHeaders. It might execute slightly faster, so the time window in which some other thread could cause the headers dictionary to be modified is narrower and the chance of encountering the InvalidOperationException is smaller, but I believe it is still nonzero.

Looking at the decompiled sources of HttpHeaders and Dictionary in .NET 4.8.1, the only reliable (but ugly) workaround I can see right now is to wrap originalRequest.Content.Headers?.ToList() in a try...catch(InvalidOperationException) and retry if the exception happens.

[peombwa]

Thanks @jberezanski-mdg for the suggestion. That's right! Adding a retry once on InvalidOperationException appears to be the only viable workaround for .NET Framework. This shouldn't be an issue for customers running on PowerShell 7.x (.NET 7).