[skrifa] use hdmx table if available

[dfrg]

In ScaledOutline::adjusted_advance_width() prefer widths from hdmx over phantom points to better match FreeType.

[drott]

LGTM, this would benefit from a test, but in the interest of getting this into a release, I am okay with doing this in a follow-up. This will have some coverage in Chromium's web tests.

[dfrg]

I'll add tests for adjusted advance width in fauntlet after I address the problem with empty glyphs. I can also add a unit test when I find a font with an hdmx table that has known provenance.