[FP5] Restrict USB

Restrict USB is not working properly on FP5 based on Android 15 (unreleased as of this writing). Regardless of settings, USB is always allowed.

Creating an independent issue for this to more easily track its progress and other details, due to its complexity thus far.

This does not affect 5.14.2, the current stable release as of this writing.

Further testing revealed that this does indeed affect previous versions of CalyxOS for the Fairphone 5. Please see our security disclosure.

Steps to reproduce

1. Change Settings > Security & privacy > More security and privacy settings > Restrict USB to "Deny [...]"
2. Unplug USB and plug it back in.

Expected result

There is no USB notification. USB debugging doesn't work, nor do other USB features (except for charging).

Actual result

USB is fully functional.