Introduce visiblePositionOf() for Position and PositionInComposedTree

Source/core/editing/VisibleSelection.h

Index: Source/core/editing/VisibleSelection.h
diff --git a/Source/core/editing/VisibleSelection.h b/Source/core/editing/VisibleSelection.h
index b1a470c28b3dd1bc69aa2c81f15e1f65df26d217..0b4db45b9fbc0145beadc8535fd6aada9f8b2ca7 100644
--- a/Source/core/editing/VisibleSelection.h
+++ b/Source/core/editing/VisibleSelection.h
@@ -82,11 +82,11 @@ public:
         static SelectionType selectionType(const VisibleSelection& selection) { return selection.selectionTypeInComposedTree(); }
         static VisiblePosition selectionVisibleStart(const VisibleSelection& selection)
         {
-            return VisiblePosition(selectionStart(selection), isRange(selection) ? TextAffinity::Downstream : selection.affinity());
+            return visiblePositionOf(selectionStart(selection), isRange(selection) ? TextAffinity::Downstream : selection.affinity());
         }
         static VisiblePosition selectionVisibleEnd(const VisibleSelection& selection)
         {
-            return VisiblePosition(selectionEnd(selection), isRange(selection) ? TextAffinity::Upstream : selection.affinity());
+            return visiblePositionOf(selectionEnd(selection), isRange(selection) ? TextAffinity::Upstream : selection.affinity());
         }
         static PositionType toPositionType(const Position& position) { return toPositionInComposedTree(position); }
     };