b40bcde0 made writing .odp use style:font-name
and office:font-face-decls, instead of using fo:font-family . But the reading
back was broken, as xFontDecls is not set
in XMLTextImportPropertyMapper::handleSpecialItem(), so the font data was
ignored. And xFontDecls was not set because it's set while reading
office:font-face-decls, which is at the top of the xml document, but even
before the xml is parsed, the call to SdXMLImport::setTargetDocument() calls
GetShapeImport(), which creates XMLShapeImportHelper instance, which calls
XMLTextImportHelper::CreateParaExtPropMapper(), and XMLTextImportPropertyMapper
is created with rImport.GetFontDecls() still being NULL at that point.

And it actually doesn't seem to make any sense to just pass around all
the pointers to XMLFontStylesContext, as eventually it's always just the one
from SvXMLImport. So simply dump all that and make the one single place
that actually uses it (i.e. XMLTextImportPropertyMapper::handleSpecialItem())
refer directly to SvXMLImport::GetFontDecls().

Change-Id: Ib1b3e4b1bcaf87ca3e4703d1cc1563ad6b3f9ce7