Styling changes for ClearAllButton

- The new style is a Widget.DeviceDefault.Button with tweaked corner radius, min size and color
- Light: http://screen/4aTR7DKuhADn2Z6
- Dark: http://screen/68XkvaAqRivbDw8

Bug: 194194694
Bug: 197887431
Test: manual
Change-Id: I1e0f2217a424a244d729c1f952035615ba045d5a

quickstep/res/drawable/bg_overview_clear_all_button.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+     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.
+-->
+<ripple android:color="?android:attr/colorControlHighlight"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:androidprv="http://schemas.android.com/apk/prv/res/android">
+    <item>
+        <shape android:shape="rectangle"
+            android:tint="?colorButtonNormal">
+            <corners android:radius="18dp" />
+            <solid android:color="?androidprv:attr/colorSurface"/>
+        </shape>
+    </item>
+</ripple>

quickstep/res/layout/overview_clear_all_button.xml

@@ -16,7 +16,7 @@
 -->
 <com.android.quickstep.views.ClearAllButton
     xmlns:android="http://schemas.android.com/apk/res/android"
-    style="@android:style/Widget.DeviceDefault.Button.Borderless"
+    style="@style/OverviewClearAllButton"
     android:id="@+id/clear_all"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"

quickstep/res/values/styles.xml

@@ -135,6 +135,13 @@
         <item name="android:textAllCaps">false</item>
     </style>
 
+    <style name="OverviewClearAllButton" parent="@android:style/Widget.DeviceDefault.Button">
+        <item name="android:background">@drawable/bg_overview_clear_all_button</item>
+        <item name="android:minWidth">85dp</item>
+        <item name="android:minHeight">36dp</item>
+        <item name="android:stateListAnimator">@null</item>
+    </style>
+
     <!-- Icon displayed on the taskbar -->
     <style name="BaseIcon.Workspace.Taskbar" >
         <item name="iconDisplay">taskbar</item>