[ExposedDropdownMenu] Fixed android:popupBackground not working in xml/styles for the AutoCompleteTextView.

Before, its value was being overwritten in code where we set the default popup background, so we should null it in the Material styles.

PiperOrigin-RevId: 437813304

Author: leticiarossi

lib/java/com/google/android/material/textfield/DropdownMenuEndIconDelegate.java

@@ -331,7 +331,7 @@ private void showHideDropdown(@Nullable AutoCompleteTextView editText) {
   }
 
   private void setPopupBackground(@NonNull AutoCompleteTextView editText) {
-    if (IS_LOLLIPOP) {
+    if (IS_LOLLIPOP && editText.getDropDownBackground() == null) {
       int boxBackgroundMode = textInputLayout.getBoxBackgroundMode();
       if (boxBackgroundMode == TextInputLayout.BOX_BACKGROUND_OUTLINE) {
         editText.setDropDownBackgroundDrawable(outlinedPopupBackground);

lib/java/com/google/android/material/textfield/res/values-v21/styles.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright 2022 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
+  ~
+  ~     https://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.
+  -->
+<resources>
+  <!-- Base style for AutoCompleteTextView. You should use one of the sub-styles instead. -->
+  <style name="Base.Widget.MaterialComponents.AutoCompleteTextView" parent="Base.V14.Widget.MaterialComponents.AutoCompleteTextView">
+    <item name="android:popupBackground">@null</item>
+  </style>
+</resources>

lib/java/com/google/android/material/textfield/res/values/styles.xml

@@ -200,8 +200,8 @@
     <item name="android:paddingBottom">13dp</item>
   </style>
 
-  <!-- Base style for AutoCompleteTextView. You should use one of the sub-styles instead. -->
-  <style name="Base.Widget.MaterialComponents.AutoCompleteTextView" parent="Widget.AppCompat.AutoCompleteTextView">
+  <!-- Base styles for AutoCompleteTextView. You should use one of the sub-styles instead. -->
+  <style name="Base.V14.Widget.MaterialComponents.AutoCompleteTextView" parent="Widget.AppCompat.AutoCompleteTextView">
     <item name="enforceMaterialTheme">true</item>
     <item name="enforceTextAppearance">true</item>
     <item name="android:background">@null</item>
@@ -218,6 +218,8 @@
     <item name="android:popupElevation" tools:ignore="NewApi">@dimen/mtrl_exposed_dropdown_menu_popup_elevation</item>
   </style>
 
+  <style name="Base.Widget.MaterialComponents.AutoCompleteTextView" parent="Base.V14.Widget.MaterialComponents.AutoCompleteTextView"/>
+
   <!-- Styles for the AutocompleteTextView to be used if an ExposedDropdownMenu style is being used. -->
   <style name="Widget.MaterialComponents.AutoCompleteTextView.FilledBox" parent="Base.Widget.MaterialComponents.AutoCompleteTextView">
     <!-- Padding values that total 34dp to visually match the spec. -->