cp#1000039 DOC import: ignore symbol charset of the symbol font

Otherwise characters unhandled by our OpenSymbol font (like Arabic 0-9
numbers) won't be rendered using an other font, as no other font
provides the symbol charset. Do this in
SwWW8ImplReader::GetFontParams(), where we already have font name ->
font family mappings for a few well-known fonts.

The DOCX filter does the same for quite some time, and that's how Arabic
numbers in text using the Symbol font were rendered, instead of little
rectangles.

Change-Id: Ib794cac19ad7b073e39f3cbd7d4bad3994151c14