Include System Apps in App Exclusion List

[binomnom]

Describe the bug
While connected to MozillaVPN, people I call complain of bad connection and dropped audio. If I disconnect from VPN, the issue disappears. I suspect it's because of VoLTE / VoWiFi connections being routed through the tunnel.

VPN version:
2.27.0 (2.202504112158)

Affected Platforms:
Android 15 (GrapheneOS build 2025041100)

Prerequisites:
Turn on VoLTE

Steps to reproduce:
Call someone, stay on the phone for a couple of minutes.

Additional notes:
Full disclosure, I have not troubleshooted this in depth. These are just my observations and thoughts collected over about 40 frustrating calls in about half a year.

I am connected to the closest server geographically to minimise latency.

The issue is somewhat intermittent and does not always present itself, but is not dependent on cell connection quality.

My proposed solution as per the title would be to show system apps in the app exclusion list. That way I could exclude dialer from being routed through the tunnel. A similar suggestion has also been made in #6604 before.

[lesleyjanenorton]

We used to have an option to show system apps on Android, I'm not sure why it was removed. @albionx what say thee about restoring this option?