Improve Dual-SIM support

Dual SIM phones are nice, but while they work more or less in SFOS, there’s room for improvement in some areas:

  1. Bluetooth HFP etc: A more or less random SIM is selected for outgoing calls (apparently it’s the “last active” SIM). This should be selectable in Bluetooth Settings. A global option would be sufficient, an additional per-pairing setting would be super nice. Asking per-connection is no-go (think cars).
  2. Seeing which SIM is which: Currently SIM card are hard coded as SIM1 and SIM2 in the UI. They should have user-friendly (user-set) names so it’s possible to see which does which.
  3. Documentation and instrumentation for developers to use the dual SIMs should be improved.

There are numerous suggestions on that in the old forum. I had spent quite some time on mine, which is pretty detailed.

The final two: