We use Liberation Sans for the actual glyph for these, and that's
missing some (Symbol) / all (ZapfDingbats) of the glyphs we need
for these two standard fonts (...or at least the mapping from
name to glyph, not sure). But still, better rendering squares than
completely incorrect glpyhs.
Our code deciding what to do when a value isn't found in an encoding,
or when the name doesn't map to a glpyh, also needs work, but that's
mostly independent of this change. I think this is a nice small
standalone progression.
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