...similar to handling breaks before shapes in lcl_startShape.

Three different examples found to create/split a paragraph.
Which one to use? (addDummy, m_bIsSplitPara, and
lcl_startCharacterGroup). SplitPara is not good because the
paragraph properties probably should not be copied to the
dummy paragraph (like numbering for example). Slightly
modified the lcl_startChar example to ensure that the dummy
paragraph doesn't steal a part of the properties, but is
only default properties plus page-break.

This doesn't export very well, so roundtripping is very poor.

Research Note: There exists a compat flag showBreaksInFrames
(Display Page/Column Breaks Present in Frames)
"This element specifies whether applications should
honor the presence of page and/or column breaks which are
present within the contents of paragraphs which have been
defined as frames using the framePr element."
--Currently, LO does nothing with this flag. Probably too
exotic and irrelevant (word 2003 era?).

No existing unit tests found that have isSet(pg_brk) frames.

Change-Id: I29f815355401c7af8b347a3ed9d0298bc9b27b93
Reviewed-on: https://gerrit.libreoffice.org/71255
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>