Reviewed by Adam Barth.

        Re-organize position creation functions in preparation for adding more
        https://bugs.webkit.org/show_bug.cgi?id=25494

        Make position functions inline to avoid ref-churn.
        Remove startPosition/endPosition as they were only used in one place.

        No functional changes, thus no tests.

        * dom/Position.cpp:
        * dom/Position.h:
        (WebCore::positionBeforeNode):
        (WebCore::positionAfterNode):
        * editing/SelectionController.cpp:
        (WebCore::SelectionController::moveTo):
        * editing/TypingCommand.cpp:
        * editing/htmlediting.cpp:
        * editing/htmlediting.h:
        (WebCore::firstDeepEditingPositionForNode):
        (WebCore::lastDeepEditingPositionForNode):
        * rendering/RenderObject.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48233 268f45cc-cd09-0410-ab3c-d52691b4dbfc