Fix -Wtype-equality-requires-operators warnings

GHC 9.4 adds `-Wtype-equality-requires-operators` to `-Wall`, which warns about
certain uses of type equalities that are not forward-compatible with planned
changes in GHC. See [this
section](https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.4?version_id=b60e52482a666d25638d59cd7e86851ddf971dc1#-is-now-a-type-operator)
of the GHC 9.4 Migration Guide. These warnings are easily fixed by enabling the
`TypeOperators` extension.

what4/src/What4/Protocol/VerilogWriter.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-
 Module           : What4.Protocol.VerilogWriter.AST
 Copyright        : (c) Galois, Inc 2020

what4/src/What4/Solver/CVC5.hs

@@ -15,6 +15,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 
 module What4.Solver.CVC5
   ( CVC5(..)

what4/src/What4/Solver/Z3.hs

@@ -14,7 +14,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
-
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE GADTs #-}
 module What4.Solver.Z3
   ( Z3(..)

what4/src/What4/Utils/OnlyIntRepr.hs

@@ -8,6 +8,7 @@ Defines a GADT for indicating a base type must be an integer.  Used for
 restricting index types in MATLAB arrays.
 -}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE TypeOperators #-}
 module What4.Utils.OnlyIntRepr
   ( OnlyIntRepr(..)
   , toBaseTypeRepr

what4/test/InvariantSynthesis.hs

@@ -3,6 +3,7 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 
 import           ProbeSolvers
 import           Test.Tasty

what4/test/OnlineSolverTest.hs

@@ -12,6 +12,7 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-} -- for TestShow instance
 
 import           Control.Concurrent ( threadDelay )