Add flag to control the rollout of SoundPicker2 app SoundPicker2 will eventually replace SoundPicker. The new app uses APIs that are currently behind flags, so we're adding a new flag so later we can swap the prebuilt SoundPicker apk with SoundPicker2. Ignore-AOSP-First: resolving merge conflict of http://aosp/2788572 Bug: 293846645 Test: N/A Change-Id: I5db915ea2745e33052baec4cca3658c8216a48f5