gsk: Keep metrics hinting on when rendering

It turns out that we mispositioned glyphs with some cff fonts when metrics hinting is off, and hinting is on. Since we don't fully understand the interactions of these settings at this point, lets preserve metrics hinting as it was on the font we got.

This at least gives folks a workaround for when they experience clipped rendering with cff fonts: Turn on hint-metrics.

We forced hint metrics off here because it made Pango do some creative wfh for hex boxes at small sizes, but I've dropped that on the Pango side.