Add 'native' support for powershell/pwsh

Current situation

PowerShell is widely used on windows environments, but the support, while possible, is not handled as best as it could:

- run: |
    $ErrorActionPreference = 'stop'
    Get-Content foobar
    if ((Test-Path -LiteralPath variable:\LASTEXITCODE)) { exit $LASTEXITCODE }
  shell: pwsh -command ". '{0]'"

Desired outcome

Simple support for powershell/pwsh

- run: Get-Content foobar
  shell: pwsh