Update docs and diagnostic message for UseCorrectCasing

[liamjpeters]

PR Summary

Fixes a small regression from #1704 where incorrectly cased parameters are reported as Functions/Cmdlets. i.e.

Get-Process -name 'Code'

Resulted in a diagnostic message of:

Function/Cmdlet '-name' does not match its exact casing 'Name'.

instead of:

Parameter '-name' of function/cmdlet 'Get-Process' does not match its exact casing 'Name'.

Added some tests for the messages.

Small tweaks to rule docs too, including that the descriptions of CheckCommands and CheckOperator were transposed.

Closes #2136

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.

[liamjpeters]

I can't see anything in the rule which acts on type names