v6.0.0-alpha.16 release of PowerShellCore

Here are the major changes:

- Add `WindowsUBR` property to `Get-ComputerInfo` result
- Cache padding strings to speed up formatting a little
- Add alias `Path` to the `-FilePath` parameter of `Out-File`
- Fix the `-InFile` parameter of `Invoke-WebRequest`
- Add the default help content to powershell core
- Speed up `Add-Type` by crossgen'ing its dependency assemblies
- Convert `Get-FileHash` from script to C# implementation
- Fix lock contention when compiling the code to run in interpreter
- Avoid going through WinRM remoting stack when using `Get-ComputerInfo` locally
- Fix native parameter auto-completion for tokens that begin with a single Dash
- Fix parser error reporting for incompleted input to allow defining class in interactive host
- Add the `RoleCapabilityFiles` keyword for JEA support on Windows
