sw doc model dump: extend SwFmtFrmSize handling

Change-Id: I8b246e198f3b19e65feffb196afdecb1755a0581
DOCX import: fix <w:tblW w:type="auto"/> handling when cells have fixed widths

Commit 74c5ed19f430327988194cdcd6bdff09591a93fa (DOCX import fix for
table with auto size, 2013-06-26) correctly recognized that in case the
width type is auto, that doesn't always mean text::SizeType::VARIABLE.

However, when the size is fixed, then we should simply not do anything,
and that'll lead to the right behavior (by setting the column separators
on each row), don't try to be smart and try to set
TablePropertyMap::TABLE_WIDTH here.

Change-Id: I997b88e5fa34bbabe7c6940879c81a1d62d69043