Fix Wi-Fi Easy Connect buttons UI defects

1. Apply attr/colorAccent to button icons for theme UI control
2. Apply attr/selectableItemBackground for button tapping ripple effect
3. Use ConstraintLayout to separate ssid EditText and scan button
4. Remove ButtonPreference and add AddNetworkPreference.
   ButtonPreference's naming and design look like a general purpose UI
   component but it's not. This change refactors the code.
5. In AddNetworkPreference, use settingslib layout file
   'preference_access_point' to fix UI alignment problems.

Bug: 126964552
Bug: 125434239
Bug: 126762937

Test: manual test
      atest com.android.settings.wifi.WifiSettingsTest
Change-Id: Ib899a1e10f96bb8427ff00d6b5dfca37a0642c44

src/com/android/settings/wifi/AddWifiNetworkPreference.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2019 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.wifi;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.graphics.drawable.Drawable;
+import android.util.Log;
+import android.view.View;
+import android.widget.ImageButton;
+
+import androidx.annotation.DrawableRes;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceViewHolder;
+
+import com.android.settings.R;
+import com.android.settings.wifi.dpp.WifiDppUtils;
+
+/**
+ * The Preference for users to add Wi-Fi networks in WifiSettings
+ */
+public class AddWifiNetworkPreference extends Preference {
+
+    private static final String TAG = "AddWifiNetworkPreference";
+
+    private boolean mInitialized;
+
+    public AddWifiNetworkPreference(Context context) {
+        super(context);
+
+        setLayoutResource(com.android.settingslib.R.layout.preference_access_point);
+        setWidgetLayoutResource(R.layout.wifi_button_preference_widget);
+        setIcon(R.drawable.ic_menu_add);
+        setTitle(R.string.wifi_add_network);
+    }
+
+    @Override
+    public void onBindViewHolder(PreferenceViewHolder holder) {
+        super.onBindViewHolder(holder);
+
+        if (!mInitialized) {
+            mInitialized = true;
+
+            final ImageButton imageButton = (ImageButton) holder.findViewById(R.id.button_icon);
+            imageButton.setImageDrawable(getDrawable(R.drawable.ic_scan_24dp));
+            imageButton.setContentDescription(
+                    getContext().getString(R.string.wifi_dpp_scan_qr_code));
+            imageButton.setOnClickListener(view -> {
+                getContext().startActivity(
+                    WifiDppUtils.getEnrolleeQrCodeScannerIntent(/* ssid */ null));
+            });
+
+            final View divider = (View) holder.findViewById(
+                    com.android.settingslib.R.id.two_target_divider);
+            divider.setVisibility(View.INVISIBLE);
+        }
+    }
+
+    private Drawable getDrawable(@DrawableRes int iconResId) {
+        Drawable buttonIcon = null;
+
+        try {
+            buttonIcon = getContext().getDrawable(iconResId);
+        } catch (Resources.NotFoundException exception) {
+            Log.e(TAG, "Resource does not exist: " + iconResId);
+        }
+        return buttonIcon;
+    }
+}