feat(unnecessary_mut_passed): support &raw references

[ada4a]

changelog: [unnecessary_mut_passed]: support &raw references

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[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

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[Jarcho]

The provenance of raw pointers is preserved through casts and coercions. This means that &raw mut e coerced to *const T is not actually equivalent to &raw const e and can result in some very subtly incorrect, but still compilable, code. Because of that I'm against linting this, especially as the same lint.

[ada4a]

Oh, sure, no problem. It's just that there were already test cases with comments about the intention to eventually lint &raw mut, and so I went ahead and implemented that. But if you're saying that linting that is actually undesirable, then I'll just remove those test cases instead