PSReviewUnusedParameter: Add CommandsToTraverse option

[FriedrichWeinmann]

PR Summary

Proposed resolution of the issue of PSReviewUnusedParameter not traversing into scriptblocks of common commands such as Where-Object or ForEach-Object (#1472).

Implementation:

• Added a new rule setting: traverseList (string[]). Scriptblocks provided as parameter to one of the listed commands will also be checked for variables.
• Added Where-Object and ForEach-Object explicitly to the list of commands to traverse

Notes & Thoughts

This is currently not too refined, but works for what it does.
Does not address $using use in Invoke-Command or other edge cases (e.g. ForEach-Object -Parallel).

But it does solve the problem for the most common everyday usage and allows extensibility for people with custom needs (e.g. I'm going to explicitly include Invoke-PSFProtectedCommand).

Also does not cover special cases, such as calculated properties of Select-Object. Or scriptblocks stored in variables and later used as argument for commands that are whitelisted. Maybe more detailed configuration options needed for cases like that.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[JamesWTruher]

we're definitely going to need new validation for this behavior.
Please create tests for this.

[bergmeister]

@FriedrichWeinmann We plan to release later this month so if you could add some tests, we could potentially merge and ship this in time?

[FriedrichWeinmann]

Sorry about the delay, added tests

[bergmeister]

@FriedrichWeinmann Thanks for adding tests, whilst reviewing I just noticed that we need to document this new option.

[bergmeister]

Thanks, LGTM now.

[JamesWTruher]

looks great - thanks for adding the tests