Apply proper backward and forward transitions

Currently, we hardcode TRANSITION_FADE_THROUGH because it is the default
as of now and it is also what Settings uses. It appears to match stock's
transition animations, too.

Issue: calyxos#1743
Change-Id: Iffe19e5b4fd552aab6c5a93bc3788a27b5eba00b

src/org/lineageos/setupwizard/SubBaseActivity.java

@@ -19,6 +19,8 @@ import android.util.Log;
 
 import androidx.activity.result.ActivityResult;
 
+import com.google.android.setupdesign.transition.TransitionHelper;
+
 public abstract class SubBaseActivity extends BaseSetupWizardActivity {
 
     public static final String TAG = SubBaseActivity.class.getSimpleName();
@@ -80,6 +82,8 @@ public abstract class SubBaseActivity extends BaseSetupWizardActivity {
             finishAction(RESULT_ACTIVITY_NOT_FOUND);
         } else if (data != null && data.getBooleanExtra("onBackPressed", false)) {
             onStartSubactivity();
+            TransitionHelper.applyBackwardTransition(this,
+                    TransitionHelper.TRANSITION_FADE_THROUGH, true);
         } else {
             finishAction(RESULT_CANCELED);
         }