WIP ReviewUnusedParameter: Search through child scope

[bergmeister]

PR Summary

Fixes #1472

This is WIP as at the moment, using a parameter in another function would yield a false negative.
An alternative implementation would be to allow only specific child scopes like e.g. the ones from ForEach-Object/Where-Object. I still have to figure out what would be better/easier

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.