Add a PowerShell wrapper

[FantasqueX]

PowerShell is a modern command line shell for Windows. This patch adds a PowerShell wrapper. This version is more maintainable than bat version. There are some difference with existing bat wrapper. First, Downloaded mill is stored in $Env:LOCALAPPDATA\mill instead of $Env:%USERPROFILE%\.mill because according to
https://en.wikipedia.org/wiki/Environment_variable#Windows, %LOCALAPPDATA% is the temporary files of Applications. And folder starting with "." is not hidden in Windows. Second, argument to set mill version is changed to -MillVersion to follow PowerShell converion, just like -RelativeBasePath of Resolve-Path
https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.management/resolve-path.

[lefou]

Thank you for this contribution. Is it necessary for the script to work, that you renamed the --mill-version option to -MillVersion? Beside the fact, that this option might die in the future, since it breaks the "transparent" wrapper experience with Mill (and there are alternatives via the env variables), I think we should try to keep it the same as in all other wrapper scripts. Also, to make it easier to write tooling around it (like Metals), which can just use the same options, disregarding of the currently used platform or user preference.

[FantasqueX]

PowerShell does not support double dash parameter out of box PowerShell/PowerShell#16749

I'll change the patch to manually parse parameters just like sh script later.

[FantasqueX]

Hi, I have pushed a fix @lefou

[lefou]

Thank you, @FantasqueX