SwDoc::DelLayoutFmt: don't delete content of a draw format

In case a shape (has a draw format) has a textbox (RES_CNTNT of the draw
format), then that's just a pointer to that content, but the draw format
doesn't own it: the matching fly format does. So ignore that content
when deleting the layout format in case of draw formats: that ensures
when both the draw and the fly format is deleted, deletion is only
performed once.

Change-Id: Idb4bb19130a6b9acd8f8d3710b9982801b416dda
SwDoc::CopyFlyInFlyImpl: factor out textbox code into SwTextBoxHelper

Also, let the new SwTextBoxHelper::restoreLinks() restore also the
RES_CNTNT of the *old* draw formats, not only the link between the new
draw and fly formats.

This allows properly preserving the link between draw and fly formats,
when they are in the header (and so copied in and out variously).

Change-Id: I101ff06533e2ea27abea8bed171ed69c9649ebe8
SwTextBoxHelper::syncProperty: handle FN_TEXT_RANGE

The TextRange property of a shape is its anchor position: if that's
adjusted, then also set the textbox's RES_ANCHOR to the new position.

Without this, e.g. shapes anchored in headers have their textboxes
anchored in the body text, CppunitTest_sw_ooxmlexport's testfdo78420 is
a reproducer.

Change-Id: I83ed09875c3f0360c581c331507ad2b9d05ffb3a