android: Replace deprecated onBackPressed() and enable predictive back gestures

Doesn't really make a difference it seems.

src/frontends/android/app/src/main/AndroidManifest.xml

@@ -37,6 +37,7 @@
         android:label="@string/app_name"
         android:theme="@style/ApplicationTheme"
         android:networkSecurityConfig="@xml/network_security_config"
+        android:enableOnBackInvokedCallback="true"
         android:allowBackup="false" >
         <activity
             android:name=".ui.MainActivity"

src/frontends/android/app/src/main/java/org/strongswan/android/ui/SelectedApplicationsActivity.java

@@ -22,6 +22,7 @@ import android.view.MenuItem;
 
 import org.strongswan.android.data.VpnProfileDataSource;
 
+import androidx.activity.OnBackPressedCallback;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.ActionBar;
 import androidx.appcompat.app.AppCompatActivity;
@@ -40,6 +41,16 @@ public class SelectedApplicationsActivity extends AppCompatActivity
 		ActionBar actionBar = getSupportActionBar();
 		actionBar.setDisplayHomeAsUpEnabled(true);
 
+		getOnBackPressedDispatcher().addCallback(this, new OnBackPressedCallback(true)
+		{
+			@Override
+			public void handleOnBackPressed()
+			{
+				prepareResult();
+				finish();
+			}
+		});
+
 		FragmentManager fm = getSupportFragmentManager();
 		mApps = (SelectedApplicationsListFragment)fm.findFragmentByTag(LIST_TAG);
 		if (mApps == null)
@@ -62,13 +73,6 @@ public class SelectedApplicationsActivity extends AppCompatActivity
 		return super.onOptionsItemSelected(item);
 	}
 
-	@Override
-	public void onBackPressed()
-	{
-		prepareResult();
-		super.onBackPressed();
-	}
-
 	private void prepareResult()
 	{
 		Intent data = new Intent();