Move isVisuallyEquivalentCandidate() to VisibleUnits.{cpp,h} from Position.{cpp,h}

Source/core/editing/VisibleUnits.h

Index: Source/core/editing/VisibleUnits.h
diff --git a/Source/core/editing/VisibleUnits.h b/Source/core/editing/VisibleUnits.h
index 8f3bfddab701a45d83705b26fd7a64028cb13dc4..c1092389d1b28d01ac5ee6af3a53acc6e365702f 100644
--- a/Source/core/editing/VisibleUnits.h
+++ b/Source/core/editing/VisibleUnits.h
@@ -66,6 +66,9 @@ CORE_EXPORT PositionInComposedTree mostForwardCaretPosition(const PositionInComp
 CORE_EXPORT Position mostBackwardCaretPosition(const Position &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
 CORE_EXPORT PositionInComposedTree mostBackwardCaretPosition(const PositionInComposedTree &, EditingBoundaryCrossingRule = CannotCrossEditingBoundary);
 
+CORE_EXPORT bool isVisuallyEquivalentCandidate(const Position&);
+CORE_EXPORT bool isVisuallyEquivalentCandidate(const PositionInComposedTree&);
+
 // words
 CORE_EXPORT VisiblePosition startOfWord(const VisiblePosition &, EWordSide = RightWordIfOnBoundary);
 CORE_EXPORT VisiblePosition endOfWord(const VisiblePosition &, EWordSide = RightWordIfOnBoundary);