Support UTF-8 with BOM for Windows PowerShell

[egasato]

It seems that powershell.exe support (in Windows) is not fully integrated.

When writing shebang recipes that use non-ASCII characters encoded in UTF-8, the output gets mangled (or more like rendered as gibberish). To support UTF-8 on Windows PowerShell, the output encoding (or codepage) has to be changed in every recipe or the file can be encoded in UTF-8 with BOM. The former is not considered ideal due to its verbose nature, and due to unintended side-effects (changing the codepage affects how the Console Window Host behaves, which means a push/pop strategy has to be used to prevent the encoding change from affecting the "caller" process).

Here's an example:

set quiet := true

default:
    #!powershell.exe -NoProfile
    Write-Host '🇪🇸 España ♥️💛♥️ just'

Here is the execution result of just default:

En C:\Users\egasato\AppData\Local\Temp\just-D1BjHk\default.ps1: 5 Carácter: 51
+ Write-Host '🇪🇸 España ♥ï¸ðŸ’›â™¥ï¸ just'
+                                                   ~
Falta la cadena en el terminador: '.
    + CategoryInfo          : ParserError: (:) [], ParseException
    + FullyQualifiedErrorId : TerminatorExpectedAtEndOfString

error: Recipe `shebang` failed with exit code 1

Here's the expected result:

🇪🇸 España ♥️💛♥️ just