Shown toast when BT turned on

* Shown "Bluetooth turned on" toast only when BT turned on in "Pair new device"
* Add test to verify shown toast function can be called when BT turned on.

Bug: 79383997
Test: make -j42 RunSettingsRoboTests ROBOTEST_FILTER=BluetoothPairingDetailTest
Change-Id: I25f75aaa04063d9ef8a0df4bb06aeaa70d7ac146

tests/robotests/src/com/android/settings/bluetooth/BluetoothPairingDetailTest.java

@@ -192,4 +192,13 @@ public class BluetoothPairingDetailTest {
         // Verify that clean up only happen once at initialization
         verify(mAvailableDevicesCategory, times(1)).removeAll();
     }
+
+    @Test
+    public void onBluetoothStateChanged_whenTurnedOnBTShowToast() {
+        doNothing().when(mFragment).updateContent(anyInt());
+
+        mFragment.onBluetoothStateChanged(BluetoothAdapter.STATE_ON);
+
+        verify(mFragment).showBluetoothTurnedOnToast();
+    }
 }