Add persistent state for Bluetooth high quality audio support

Defines the flags used in code and the Settings.Global key names for
persisting the following state for Bluetooth A2DP Sink devices:
-Whether the device supports optional codecs or not
-Whether optional codecs should be turned on for the device

For each of these two properties we model the state in the code as
yes/no/unknown, so that we can tailor the UI and behavior
accordingly.

Bug=37441685
Test: manually

Change-Id: I6bcd02fd7c95bef989575f3b13d4788dab61971a
diff --git a/core/tests/coretests/src/android/provider/SettingsBackupTest.java b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
index ad4afae..7d04954 100644
--- a/core/tests/coretests/src/android/provider/SettingsBackupTest.java
+++ b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
@@ -109,6 +109,8 @@
                     Settings.Global.BLE_SCAN_ALWAYS_AVAILABLE,
                     Settings.Global.BLUETOOTH_A2DP_SINK_PRIORITY_PREFIX,
                     Settings.Global.BLUETOOTH_A2DP_SRC_PRIORITY_PREFIX,
+                    Settings.Global.BLUETOOTH_A2DP_SUPPORTS_OPTIONAL_CODECS_PREFIX,
+                    Settings.Global.BLUETOOTH_A2DP_OPTIONAL_CODECS_ENABLED_PREFIX,
                     Settings.Global.BLUETOOTH_DISABLED_PROFILES,
                     Settings.Global.BLUETOOTH_HEADSET_PRIORITY_PREFIX,
                     Settings.Global.BLUETOOTH_INPUT_DEVICE_PRIORITY_PREFIX,