Print name prefixly in the Outputable instance for StandaloneKindSig

Issue #17461 was occurring because the `Outputable` instance for
standalone kind signatures was simply calling `ppr` on the name in
the kind signature, which does not add parentheses to infix names.
The solution is simple: use `pprPrefixOcc` instead.

Fixes #17461.

compiler/GHC/Hs/Decls.hs

@@ -1471,7 +1471,8 @@ instance OutputableBndrId p
 
 instance OutputableBndrId p
        => Outputable (StandaloneKindSig (GhcPass p)) where
-  ppr (StandaloneKindSig _ v ki) = text "type" <+> ppr v <+> text "::" <+> ppr ki
+  ppr (StandaloneKindSig _ v ki)
+    = text "type" <+> pprPrefixOcc (unLoc v) <+> text "::" <+> ppr ki
   ppr (XStandaloneKindSig nec) = noExtCon nec
 
 instance Outputable NewOrData where

testsuite/tests/th/T17461.hs

+{-# LANGUAGE StandaloneKindSignatures #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeOperators #-}
+module T17461 where
+
+import Data.Kind
+
+$([d| type (:+:) :: Type -> Type -> Type
+      type (:+:) = Either
+    |])

testsuite/tests/th/T17461.stderr

+T17461.hs:(8,3)-(10,6): Splicing declarations
+    [d| type (:+:) :: Type -> Type -> Type
+        
+        type (:+:) = Either |]
+  ======>
+    type (:+:) :: Type -> Type -> Type
+    type (:+:) = Either

testsuite/tests/th/all.T

@@ -491,3 +491,4 @@ test('T17380', normal, compile_fail, [''])
 test('T17394', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])
 test('T17379a', normal, compile_fail, [''])
 test('T17379b', normal, compile_fail, [''])
+test('T17461', normal, compile, ['-v0 -ddump-splices -dsuppress-uniques'])