areEquivalent types should be informed by the sequences they represent

Previously elementsEqual only worked with two sequences of the same
type. So this solution worked. Now that elementsEqual can compare
differing types if the predicate is supplied we must update it

Author: Cbieniak

stdlib/public/core/SequenceAlgorithms.swift.gyb

@@ -353,7 +353,7 @@ ${equivalenceExplanation}
   public func elementsEqual<OtherSequence>(
     _ other: OtherSequence${"," if preds else ""}
 %   if preds:
-    by areEquivalent: (${GElement}, ${GElement}) throws -> Bool
+    by areEquivalent: (${GElement}, OtherSequence.${GElement}) throws -> Bool
 %   end
   ) ${rethrows_}-> Bool
     where