Recommend ScopedTypeVariables

The !ScopedTypeVariables extension is one of the few that doesn't recommend itself when it should be used.

I recognize that this may be hard to do, but here is a strawman proposal: Always behave as if !ScopedTypeVariables is on at binding sites for type variables (in an annotation with forall). Then, at occurrences of type variables, check if the extension is on. If a type variable is in scope but the extension is off, remember that the user probably wants the extension, but then rename the type variable occurrence away from the in-scope one. If a type error ensues, we've remembered that the lack of !ScopedTypeVariables may be to blame, and we recommend turning it on.

There may be better approaches, too.

Trac metadata

Trac field	Value
Version	7.10.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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