Muting notifications due to focus is conditional on recording

Legacy behavior is to mute notification while an app has
requested audio focus with GAIN_TRANSIENT_EXCLUSIVE.
The new behavior under flag is to enforce that the muting
happens only when the focus requester is also recording audio.

Implementation uses a new AudioManager method that contains
all audio framework-side evaluation of whether the notification
should play, and avoid code duplication in
NotificationManagerService and NotificationAttentionHelper.

Annotated AudioAttributes field in NotificationRecord
to document that they are never null (so always available
to be consumed by AudioManager.shouldNotificationSoundPlay).

Updated unit tests to also mock AudioManager's response
for shouldNotificationPlaySound such that it's compliant
with the ringer mode and volume set on the mock in the
existing test. This way the test is independent of the flag
state.

Flag: android.media.audio.focus_exclusive_with_recording
Test: atest android.media.audio.cts.AudioFocusTest
Test: atest BuzzBeepBlinkTest NotificationAttentionHelperTest
Bug: 316414750
Change-Id: I54147c0dcccd7785589f4c9882582f42cf1a2d65