Instead of the previous approach which relied on a side effect of
installing *-fonts parts that would write in parts/fonts/ and make the
fonts automatically available to applications, use a new approach where
each part is "pure", without side effects.
To make the fonts available to applications, a fontconfig font.conf
listing all the parts with fonts needs to be generated and set as
$FONTCONFIG environment variable.

A template font.conf is included in component/fontconfig