Fix infix constructor pattern matching for normal constructors

Brittany was previously only support symbol based infix constructors. It
is common in some libraries (for example Esqueleto) to pattern match on
normal constructors as infix. Brittany was failing in this case by not
wrapping the constructor name in back ticks/spaces. Backticks and spaces
have been added in the case where the constructor contains any alpha
characters.

src-literatetests/10-tests.blt

@@ -355,6 +355,9 @@ func (x:xr) = x
 #pending
 func (x:+:xr) = x
 
+#test normal infix constructor
+func (x `Foo` xr) = x
+
 
 ###############################################################################
 ###############################################################################

src/Language/Haskell/Brittany/Internal/Layouters/Pattern.hs

@@ -13,6 +13,7 @@ where
 import           Language.Haskell.Brittany.Internal.Types
 import           Language.Haskell.Brittany.Internal.LayouterBasics
 
+import           Data.Char (isAlpha)
 import           RdrName ( RdrName(..) )
 import           GHC ( Located, runGhc, GenLocated(L), moduleNameString )
 import           HsSyn
@@ -80,7 +81,9 @@ layoutPat lpat@(L _ pat) = docWrapNode lpat $ case pat of
     let nameDoc = lrdrNameToText lname
     leftDoc  <- colsWrapPat =<< layoutPat left
     rightDoc <- colsWrapPat =<< layoutPat right
-    middle <- docLit nameDoc
+    middle <- docLit $ if Text.any isAlpha nameDoc
+      then Text.pack " `" <> nameDoc <> Text.pack "` "
+      else nameDoc
     return $ Seq.empty Seq.|> leftDoc Seq.|> middle Seq.|> rightDoc
   ConPatIn lname (RecCon (HsRecFields [] Nothing)) -> do
     -- Abc{} -> expr