haskell/highlights: Match pattern as a keyword

Sample:
-- | Smart constructor that deduplicates plugins
pattern IdePlugins :: [PluginDescriptor ideState] -> IdePlugins ideState
pattern IdePlugins{ipMap} <- IdePlugins_ (sortOn (Down . pluginPriority) . HashMap.elems -> ipMap) _
  where
    IdePlugins ipMap = IdePlugins_{ipMap_ = HashMap.fromList $ (pluginId &&& id) <$> ipMap
                                  , lookupCommandProvider = lookupPluginId ipMap
                                  }

queries/haskell/highlights.scm

@@ -81,6 +81,7 @@
   "in"
   "class"
   "instance"
+  "pattern"
   "data"
   "newtype"
   "family"