[Analyzer Proposal]: warn when calling `GetType()` on a `System.Type`

[ericstj]

I've noticed a few times where folks make a mistake through refactoring or copy-paste (or AI hallucinations) where they call GetType() on a System.Type object. This doesn't cause any compile errors since System.Type is an object and therefore has a GetType() method - but it's more often the wrong thing to do than not.

I suggest we add an analyzer that warns folks when they do this.

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