More granular orphan warning reporting

There are two use cases:

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The main case is for myself as a maintainer of "proper home for orphan" packages, like quickcheck-instances or binary-instances.

The -Worphan warns. But it's blunt. My packages give proper home for orphans, but only from QuickCheck or binary. I'd like to be able to tweak which orphans are accepted.

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Another use case, which is probably more useful for general community is defining orphan instances in tests. We often write Arbitrary instances in tests, for types from the main library. I'd like to say, that orphans are ok, as far as they are from the same package.

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A possible solution is !2932 (closed).

CC @simonpj