Use AudioManager API instead of manually checking ringing volume.

This CL ensures that the Ringer class relies on the AudioManager#shouldNotificationSoundPlay API instead of manually checking ringing volume when determining if a ringtone should be played audibly for an MT call. This CL also adds the feature flag for all of the go/ring-my-car Telecom feature work.

Bug: 348707841
Flag: com.android.server.telecom.flags.ensure_in_car_ringing
Test: atest RingerTest

Change-Id: I7df60d54e4e6e8ede69e807a6091647104ea9863
diff --git a/flags/telecom_ringer_flag_declarations.aconfig b/flags/telecom_ringer_flag_declarations.aconfig
index f126bf3..6517e0f 100644
--- a/flags/telecom_ringer_flag_declarations.aconfig
+++ b/flags/telecom_ringer_flag_declarations.aconfig
@@ -7,4 +7,12 @@
   namespace: "telecom"
   description: "Gates whether to use a serialized, device-specific ring vibration."
   bug: "282113261"
+}
+
+# OWNER=grantmenke TARGET=24Q4
+flag {
+  name: "ensure_in_car_ringing"
+  namespace: "telecom"
+  description: "Gates whether to ensure that when a user is in their car, they are able to hear ringing for an incoming call."
+  bug: "348708398"
 }
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