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Extension shuffling (#23291)

Andrei Borzenkov requested to merge sand-witch/ghc:sand-witch/modern-STV-extension-suffling into master

Fixed #23291

I introduced 4 new extensions (PatternSignatures, ExtendedForAllScope, MethodTypeVariables, ImplicitForAll) and new warning (-Wpattern-signature-binds), so I did this part of proposal #448

The changes are accordant with the proposal, except -XNoImplicitForAll also throws error when there is type variable binding in pattern signature:

ghci> f (a :: t) = a

<interactive>:6:4: error: [GHC-78543]
    Unbound type variable: ‘t’
    Suggested fix: Perhaps you intended to use ImplicitForAll

IMO, that's the right behavior of this extension, but we can discuss this.

Edited by Andrei Borzenkov

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