Installer should copy fontconfig cache to the installed system

[Paweł Stołowski]

After the installation completes, fontconfig cache files (/var/cache/fontconfig) should be copied from the live CD session to the just installed system, before reboot.

The rationale:

Snapd creates fontconfig cache files (/var/cache/fontconfig) for fontconfig cache format v6 and v7 (this is done by snapd to significantly reduce startup time for snaps that may use one of the two formats). This is a one-time operation that can take as much as ~20 seconds; it's performed on the live CD session as it runs snapd, but since the newly installed system has empty /var/cache/fontconfig after first boot, it needs to be repeated by snapd. This affects first boot experience as it has impact on readiness of snapd and snap for normal usage. Observed with 19.04 installs.

[Michael Vogt (mvo)]

Is there anything that snapd needs to do here? It already generates the caches, does it need to do more? It seems this is a ubiquity task, yes?