Make slight/rgb the default option

Medium hinting and None subpixel rendering was default options added
when we used Oxygen fonts, however freetype recommends slight hinting as
seen in this blog post from 2015 [1].

Also RGB hinting is most-recommended over the None. See linked bug
report as well.

BUG: 389598

[1] https://www.freetype.org/freetype2/docs/text-rendering-general.html