Start using PowerShell Standard 3

[bergmeister]

Summary of the new feature

Use PSStandard to simplify PowerShell references and potentially reduce the amount of binaries to ship. Because 1 rule is not available for ps v3 and v4, it might only be possible to use it for the engine project for starters. We need to explore and take it from there.

What is the latest version of PSScriptAnalyzer at the point of writing

1.17.1

[bergmeister]

Note:
Unfortunately there are lots of conditional pragmas in the engine and rule proejcts for v3,4,5 and 6 due to certain APIs being available or not.
I tried converting the engine project today to be only netstandard2.0 and PSStandard3 and there is no way how it can be converted because there is so much conditional compilation code for APIs that are or are not present in v3, v4, v5 and v6. Even when using PSStandard5.1, I had one unknown type (SemanticVersion), but this is probably a bug.