android: suppress warnings for deprecated constants in ConnectivityManager (#6835)

For Android version 28, some constants in ConnectivityManager have been deprecated such as ConnectivityManager. CONNECTIVITY_ACTION, ConnectivityManager. TYPE_WIFI, ConnectivityManager. TYPE_MOBILE, etc. In grpc-android, they are used for supporting legacy SDK connectivity state monitoring (and its unit tests). They work as intended for legacy SDK versions. So we suppress those warnings for the target SDK version 28.

Author: voidzcy

android/src/main/java/io/grpc/android/AndroidChannelBuilder.java

@@ -205,6 +205,7 @@ public void run() {
             };
       } else {
         final NetworkReceiver networkReceiver = new NetworkReceiver();
+        @SuppressWarnings("deprecation")
         IntentFilter networkIntentFilter =
             new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
         context.registerReceiver(networkReceiver, networkIntentFilter);

android/src/test/java/io/grpc/android/AndroidChannelBuilderTest.java

@@ -51,6 +51,7 @@
 @LooperMode(LEGACY)
 @RunWith(RobolectricTestRunner.class)
 @Config(shadows = {AndroidChannelBuilderTest.ShadowDefaultNetworkListenerConnectivityManager.class})
+@SuppressWarnings("deprecation")
 public final class AndroidChannelBuilderTest {
   private final NetworkInfo WIFI_CONNECTED =
       ShadowNetworkInfo.newInstance(