fdo#69613: Fix for DOCX Export loses Table-of-Contents flags

(This is partial fix for this bug includes flag 'f' processing)

Issue description:
Export logic for all TOC field flags was enclosed inside
if( nsSwTOXElement::TOX_MARK & pTOX->GetCreateType() ) in ww8atr.cxx,
which gets true for 'f' flag, this was the reason if there is 'f' flag
present in original doc then only other flags like \o \h used to come after RoundTrip.

Added Unit test case to verify even if there is no 'f' flag in original doc,other flags
eg. \h is getting preserved after RT.

Conflicts:
	sw/source/filter/ww8/ww8atr.cxx
Reviewed on:
	https://gerrit.libreoffice.org/7203

Change-Id: I29d22b363cc91ae5fabffca959786134bf1ba1cc