Add sw::IsParaPropsNode() to check if the node's numbering attributes are
effective in the given layout.

Add IDocumentOutlineNodes::isOutlineInLayout() to expose this to UI code.

Adapt IDocumentOutlineNodes::getOutlineText() to produce the merged text
of the outline paragraph as seen in the layout.

Also adapt EnhancedPDFExport and SwFieldRefPage to interface changes.

Change-Id: I6fa95150ff0c5dc5eb4f366d218e8f0c4d4bb7ab