fix: We now properly notify Jbang we're running in PowerShell

`JBANG_USES_POWERSHELL=true` was set too late for Jbang to pick it up.
It also fixes the fact that jbang on Windows wasn't properly delegating
to the downloaded version when using "zero install".

Fixes quarkusio#401

src/main/scripts/jbang.cmd

@@ -33,6 +33,8 @@ if exist "%~dp0jbang.jar" (
     if !ERRORLEVEL! NEQ 0 ( echo Error installing JBang 1>&2 & exit /b %ERRORLEVEL% )
     ren "%TDIR%\jars\jbang.tmp" "jbang"
   )
+  call "%TDIR%\jars\jbang\jbang\bin\jbang.cmd" %*
+  exit /b %ERRORLEVEL%
 )
 
 rem Find/get a JDK

src/main/scripts/jbang.ps1

@@ -76,6 +76,8 @@ if (Test-Path "$PSScriptRoot\jbang.jar") {
     }
     Rename-Item -Path "$TDIR\jars\jbang.tmp" -NewName "jbang" >$null 2>&1
   }
+  . "$TDIR\jars\jbang\jbang\bin\jbang.ps1" $args
+  break
 }
 
 # Find/get a JDK
@@ -129,14 +131,14 @@ if ($JAVA_EXEC -eq "") {
   }
 }
 
+$env:JBANG_USES_POWERSHELL="true"
 $output = & $JAVA_EXEC $env:JBANG_JAVA_OPTIONS -classpath "$jarPath" dev.jbang.Main $args
 $err=$LASTEXITCODE
 
 $erroractionpreference=$old_erroractionpreference
 $global:progresspreference=$old_progresspreference
 
 if ($err -eq 255) {
-  $env:JBANG_USES_POWERSHELL="true"
   Invoke-Expression "& $output"
 } else {
   Write-Output $output