Update/standardize the internal custom `VariableAnalysis` classes

This addresses technical debt.

... the VariableAnalysis classes that were forked from PowerShell's own classes 4 years ago. Those classes were not updated since and have small bugs that leads to certain types of analysis not being possible. Unfortunately, the original maintainers have taken only a subset of it and added a lot of custom code to it. I once tried to just delete it and replace it with the code from PowerShell and some of the challenges were that SMA are very entangled with each other in terms of dependencies and it compiles against .Net Core, but PSSA compiles against .Net Standard.

(https://github.com/PowerShell/PSScriptAnalyzer/pull/1277#issuecomment-508929230)

Commencez par lire la discussion liée dans PowerShell/PSScriptAnalyzer#1277 et identifiez les classes internes de VariableAnalysis ainsi que leurs dépendances. Comparez les classes forkées avec les versions de PowerShell en tenant compte des cibles de compilation .NET Core et .NET Standard. Le travail est considéré comme terminé lorsque la dette technique, les bogues d’analyse connus et les contraintes liées aux dépendances ou au framework sont traités sans casser l’analyseur.