Make isInsolubleOccursCheck more aggressive
Consider type family F a :: * -> * Then (a ~ F Int a) is an insoluble occurs check, and can be reported as such. Previous to this patch, TcType.isInsolubleOccursCheck was treating any type-family application (including an over-saturated one) as unconditionally not-insoluble. This really only affects error messages, and then only slightly. I tripped over this when investigating Trac #13674.
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