updating the path resolution with new sampler public functions and fixing some issues

[gaelcolas]

Fixed

• Fixed #247 where Building submodule would fail on linux (but not WSL).
• Fixed #239 to re-add support for BuiltModuleSubdirectory more consistently.

Changed

• Refactored a lot of Path resolution into Sampler public function for consitency and re-usability.

• Updated the Tasks to use those Sampler functions.

• Updated Get-BuiltModuleVersion to support $BuiltModuleSubdirectory as per #239.

  Added

• Added Get-SamplerAbsolutePath, Get-SamplerBuiltModuleBase, Get-SamplerModuleInfo, Get-SamplerBuiltModuleManifest, Get-SamplerModuleRootPath.

Notes

Once (pre)released here, the DscResource.DocGenerator module will have to be updated for its tasks. There's a small breaking change with Get-BuiltModuleVersion. /cc @johlju

---

This change is