Move Magnification Mode Settings to the main page

We move the mode settings because currently there is
only one item in the settings page. To fully test all logic,
we don't use fragament anymore in the controllerTest, and
test the interaction between the controller and the fragment
in the test of these two fragments.

Bug: 182992338
Test: atest ToggleScreenMagnificationPreferenceFragmentTest
      atest MagnificationModePreferenceControllerTest
      atest MagnificationSettingsFragmentTest
      manually test
Change-Id: Ia6b0ea4f116f3215407637d7aeaddb8d8196d8fb

tests/robotests/src/com/android/settings/testutils/shadow/ShadowSettingsPreferenceFragment.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.testutils.shadow;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.android.settings.SettingsPreferenceFragment;
+
+import org.robolectric.annotation.Implementation;
+import org.robolectric.annotation.Implements;
+
+/**
+ * Shadow of {@link SettingsPreferenceFragment}.
+ *
+ * Override the {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}} to skip inflating
+ * a View from a xml.
+ */
+@Implements(SettingsPreferenceFragment.class)
+public class ShadowSettingsPreferenceFragment extends ShadowFragment {
+
+    @Implementation
+    public View onCreateView(LayoutInflater inflater, ViewGroup container,
+            Bundle savedInstanceState) {
+        return container;
+    }
+}