fdo#69613: Code changes for TOC with flag '\x' should get preserved after RT.

Issue :
	TOC field flag '\x' was not getting preserved after RT.

Implementation :
	Provided import & export support for TOC field flag '\x'.

XML file difference :
	In document.xml,

Before:
	‒<w:r w:rsidR="00A9725D">
	‒<w:instrText xml:space="preserve">
	  TOC \o "1-3"
	</w:instrText>
	</w:r>
	‒<w:r w:rsidR="008A34F6">
	‒<w:instrText>
	  \h
	</w:instrText>
	</w:r>
	‒<w:r w:rsidR="00A9725D">
	‒<w:instrText xml:space="preserve">
	  \x
	</w:instrText>
After:
	‒<w:instrText>
	  TOC \x \o "1-3" \h
	</w:instrText>

Conflicts:
	sw/inc/tox.hxx
	sw/inc/unoprnms.hxx
	sw/source/core/unocore/unoidx.cxx
	sw/source/core/unocore/unomap.cxx
	sw/source/filter/ww8/ww8atr.cxx
	sw/source/ui/index/cntex.cxx
	writerfilter/source/dmapper/DomainMapper_Impl.cxx
	writerfilter/source/dmapper/PropertyIds.cxx
	writerfilter/source/dmapper/PropertyIds.hxx
Reviewed on:
	https://gerrit.libreoffice.org/7257

Change-Id: I8f196446a3beb8deea6b7ddde50e16c9cea73cd9