Needs fontconfig integration

Status changed to 'Confirmed' because the bug affects multiple users.

I confirm that these are needed, at least for Java Swing applications.
They crash without this with a NullPointerException at sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1264).

I also needed to add these variables to package a Racket/Scheme game that I made several years ago.

I also needed to bundle some fonts with the snap, namely fonts-dejavu. Without them, instead of letters, only rectangles were displayed. In case of Java, it didn't even start.

Snapcraft should handle these variables.
I also think that snapd should grant access to the fonts and fontconfig directories/files of the system and user. That would be really useful for things like LibreOffice.

Snapcraft applications should use their own fontconfig files, not from host system because of compatibility issues. I made a snap for application that is no longer in repositories. My host OS is 20.04 and snap base OS is 18.04. This causes incompatibilities between snaps and system.

Workaround for this issue:
(in apps section)
apps:
  some_app:
    command: some_app
    environment:
      XDG_DATA_HOME: $SNAP/usr/share
      FONTCONFIG_PATH: $SNAP/etc/fonts/conf.d
      FONTCONFIG_FILE: $SNAP/etc/fonts/fonts.conf

Of course this only works in devmode. After switching to strict mode program in snap ends with error that it can't reach /etc/fonts/fonts.conf file. I think should be resolved by adding interface.

This will probably be a part of larger work related to picking up bits of /etc from the host.