Remove shadow on Add button

Set android:stateListAnimator to @null to remove default shadow on Add
button.

Bug: 333736273
Test: manual, check shadow on device
Flag: ACONFIG com.android.launcher3.enable_widget_tap_to_add NEXTFOOD
Change-Id: Ifa66801963e69582935806eb8a39dcfe624ffdc7
diff --git a/res/layout/widget_cell_content.xml b/res/layout/widget_cell_content.xml
index 462bb52..b6412db 100644
--- a/res/layout/widget_cell_content.xml
+++ b/res/layout/widget_cell_content.xml
@@ -107,6 +107,7 @@
             android:drawablePadding="@dimen/widget_cell_add_button_drawable_padding"
             android:drawableTint="?attr/widgetPickerAddButtonTextColor"
             android:maxLines="1"
+            style="@style/Button.Rounded.Colored"
             android:background="@drawable/widget_cell_add_button_background" />
     </FrameLayout>
 </merge>