Instead of Microsoft.PowerShell.Linux.Host
Since this changes the name of the library,
System.Management.Automation's assembly info needed to be updated.
- Pester source code moved to `test/Pester`, deleted `ext-src`.
- Pester tests (.ps1 files) moved to `test/powershell`
- xUnit tests (.cs files) moved to `test/csharp`
- Third-party script test moved to `test/shebang`
PSRP will of course still require it, but now the managed host sets up
the assembly load context, meaning we can depend on the emitted binary
from dotnet-cli.
Andrew Schwartzmeyer