Add FreeBSD support

[Thefrank]

PR Summary

• Adds platform detection support for FreeBSD
• Adds a FreeBSD test
• Updates a few existing tests to be executed under FreeBSD

PR Checklist

• PR has meaningful title
• Summary describes changes
• PR is ready to be merged
• Tests are added/update (if required)
• Documentation is updated/added (if required)

A few notes

• This PR should not be merged until Fix FreeBSD build failures. Update tests for FreeBSD PowerShell/PowerShell-Native#92 and WIP: Add platform support for FreeBSD PowerShell/PowerShell#20041 are merged. The first fixes the build and test issues of the native library PS uses so it works under FreeBSD the second one adds build and operation support to PS under FreeBSD
• FreeBSD has a platform in dotNET and community support for building/using it.
• Tests were executed against my fork (pending PR) of Powershell port for FreeBSD (https://github.com/Thefrank/PowerShell/tree/freebsd). build ./build.ps1 -Clean -Inline. test: Import-Module .\bin\Pester.psd1 -Force then ./test.ps1 -CI -PassThru -NoBuild
  • Two tests report a single failure: Pester.RSpec.InNewProcess.ts.ps1 and Pester.RSpec.Output.ts.ps1
    • RSpec.InNewProcess: Keeps original exit code from Invoke-Pester fails returning a "Check the spelling" instead of the expected ExitCode=2
    • RSpec.Output: Multiline string has ansi style at start of every line and reset at end of last line fails returning a '\Hello World\' is not recognized as a name of a cmdlet

[nohwnd]

LGTM so far.