Moving PowerShell to .NET 5 via branch https://github.com/SteveL-MSFT/PowerShell/tree/dotnet-5

We have tests that expect the pwsh process to have a ProcessName of pwsh, but on Linux, the name is actually ConsoleHost mai (looks to be cut off). Works correctly on Windows and macOS.

Note that [System.AppDomain]::CurrentDomain.FriendlyName returns pwsh as expected.