Change Position to pre-compute the AnchorType and store it.
        Also store a "legacy editing mode" bit on the Position.
        https://bugs.webkit.org/show_bug.cgi?id=24763

        The old Postion(node, offset) constructor creates legacy positions
        but there are new constructors to create explicitly anchored positions
        which the next patch will use.

        Once we fix all the "position-fixup" functions (like rangeCompliantEquivalent) to
        only affect legacy positions, we will be able to distinguish
        between [table, 1] and [table, after] in the code correctly!

        * WebCore.base.exp:
        * WebCore.xcodeproj/project.pbxproj:
        * dom/Position.cpp:
        (WebCore::Position::Position):
        (WebCore::Position::moveToPosition):
        (WebCore::Position::moveToOffset):
        (WebCore::Position::anchorTypeForLegacyEditingPosition):
        (WebCore::Position::element):
        * dom/Position.h:
        (WebCore::Position::):
        (WebCore::Position::Position):
        (WebCore::Position::anchorType):
        (WebCore::Position::deprecatedEditingOffset):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@43075 268f45cc-cd09-0410-ab3c-d52691b4dbfc