This fixes the inability to insert a numbered Heading into
an existing sequence in an opened document. Before it would
start a new sequence, but now it connects to / adjusts
the other numbered Headings.

LibreOffice has built-in handling for "Chapter Numbering".
All of the formatting for this is tied to the paragraph stylename.

Since MSO has a different structure, in docx format these
are defined as "regular" styles with an OutlineLvl component.
During import, that style information was copied to LO's special
Outline chapter numbering style. *From this point on, the
"regular" list style should no longer be referred to.* Numbering is only
defined by the paragraph stylename (which by definition is "Heading X").

The unit test I am hijacking has an unchangeable Paragraph Numbering
style of "Outline Numbering" and not WWNumX. So, in reality the
document ought to require the style name to be the internal Outline
style like it originally was.
A followup patch allows this to round-trip.

Change-Id: If5d544529fa32d4abaa2b46403bc61c028e53f21
Reviewed-on: https://gerrit.libreoffice.org/47827Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>