Split battery header text to a separated preference

This is a no-op refactor. This change makes the Catalyst migration of battery level bar easy.

Bug: 372774754
Test: manual
Flag: EXEMPT bug fix
Change-Id: I6e64e6d9b34aeca584f4d4e951c58c3e1b361f9d

res/layout/preference_battery_header_text.xml

@@ -0,0 +1,32 @@
+<!--
+  ~ Copyright (C) 2024 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.
+  -->
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:orientation="vertical"
+    android:layout_marginStart="?android:attr/listPreferredItemPaddingStart"
+    android:layout_marginEnd="?android:attr/listPreferredItemPaddingEnd"
+    android:paddingBottom="16dp">
+
+    <TextView
+        android:id="@+id/text"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:ellipsize="marquee"
+        android:textAppearance="@*android:style/TextAppearance.DeviceDefault.Body1"
+        android:textSize="14sp"/>
+</LinearLayout>

res/xml/power_usage_summary.xml

@@ -25,8 +25,14 @@
         android:key="battery_header"
         android:title="@string/summary_placeholder"
         android:selectable="false"
+        android:paddingBottom="0px"
         settings:controller="com.android.settings.fuelgauge.BatteryHeaderPreferenceController" />
 
+    <com.android.settings.fuelgauge.BatteryHeaderTextPreference
+        android:key="battery_header_text"
+        android:selectable="false"
+        settings:controller="com.android.settings.fuelgauge.BatteryHeaderTextPreferenceController" />
+
     <com.android.settingslib.widget.LayoutPreference
         android:key="battery_help_message"
         android:layout="@layout/preference_battery_error"