call ring goes only to connected headset

Description

Overview

For incoming calls, ringer should sound on mobile-device speakers, even if Bluetooth headset is connected.

The reason is that a user may have recently spoken on a call using a headset, then removed the headset, without ending the connection between the headset and the mobile device. In this case, because the ringer sound currently only occurs through the headset, the user would not have effective audio indication of an incoming call. The native system for processing regular incoming telephone calls produces sound on both the mobile-device internal speakers as well as any connected headset. As this behavior is generally desirable, Signal application should follow the same pattern.

Steps to Reproduce

1. Connect Bluetooth headset.
2. Receive incoming call.
3. Notice that audio notification occurs through headset but not mobile-device internal speakers. Thus, effective audio indication of incoming call depends on user currently wearing headset.

Device

Device: LG Nexus 4
Android version: 9 (Resurrection Remix 7.0.2)
Signal version: 5.3.12

No source file, test, or entry point is named. Start with the listed Bluetooth-headset reproduction steps and trace incoming-call audio routing; done means the ringer is audible from the mobile-device speakers as well as any connected headset.