DOCX import: fix handling of embedded DOCX files

The problem was that SwXTextEmbeddedObject::getEmbeddedObject() returned
an empty reference for those embedded objects, so the HTML filter
couldn't extract their content when it wanted to do so.

It turns out the reason for this was that the DOCX importer only handled
the replacement image + raw native data for the object. Fix this by
creating the embedded object with the correct CLSID and import the
raw data into the empty embedded document model.

This is similar to what is done for XLSX-in-PPTX in
oox::drawingml::ShapeExport::WriteOLE2Shape(), just for the import part.

(cherry picked from commit 41aa970b3120837ca9cadb12997a53ad322145a4)

Conflicts:
	writerfilter/source/dmapper/OLEHandler.cxx
	writerfilter/source/dmapper/OLEHandler.hxx

Also squash in 3 fixes on top of that in the HTML filter which are
relevant only after the embedded DOCX import is fixed:

1) sw HTML export: don't crash on embedded object without native data

(cherry picked from commit 35e954149d976e0e69a9f8b382fc67f5abc5eaa7)

2) sw HTML export: handle embedded text documents

(cherry picked from commit 8d670c9452e930460be600212d73e22acd61cc0f)

3) sw HTML export: avoid invalid output for embedded documents

When an sw document is embedded inside an sw one, then the inner sw HTML export
should just write what's inside the <body>. Add a filter option for that in sw,
similar to the one already existing in sc.

(cherry picked from commit 8760b2b05c23e5fdf8ad7ad3f447a7489c2ddeac)

Conflicts:
	sw/source/filter/html/wrthtml.cxx

Change-Id: Id2cef966c1022ba45a3540bff234029c1d396778
Reviewed-on: https://gerrit.libreoffice.org/11151
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Tomaž Vajngerl <quikee@gmail.com>
Resolves: icu#11100 resolveImplicitLevels woes

Change-Id: I0c052cbcfe375bd1279c2235b53c909920e2e779
(cherry picked from commit 5d952d4208aa61b6bb0c20d36745d0554be7cec3)
Reviewed-on: https://gerrit.libreoffice.org/11129
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>