Reviewed by Ryosuke Niwa.

        Move the MouseEventWithHitTestResults::targetNode() method on to EventHandler.
        https://bugs.webkit.org/show_bug.cgi?id=57921

        Moves the MouseEventWithHitTestResults::targetNode() method on to EventHandler, so
        that the same logic can be used for a HitTestResult.

        No visible changes, just cleanup, so no tests.

        * page/EventHandler.cpp:
        (WebCore::EventHandler::selectClosestWordFromMouseEvent):
        (WebCore::EventHandler::selectClosestWordOrLinkFromMouseEvent):
        (WebCore::EventHandler::handleMousePressEventTripleClick):
        (WebCore::EventHandler::handleMousePressEventSingleClick):
        (WebCore::EventHandler::handleMousePressEvent):
        (WebCore::EventHandler::handleMouseDraggedEvent):
        (WebCore::EventHandler::handleMouseReleaseEvent):
        (WebCore::EventHandler::subframeForHitTestResult):
        Made public static member, so that it c...