Fix missing DesktopWallpaperActivity in DW

- Added `android:showForAllUsers` activity flag to enable the activity
  to be shown for all users.
- More details: b/346754065#comment3

Bug: 346754065
Test: manual
Flag: com.android.window.flags.enable_desktop_windowing_wallpaper_activity
Change-Id: I4c62d92ccdd98a337d1e1a72f92c6216919d8e34
diff --git a/libs/WindowManager/Shell/AndroidManifest.xml b/libs/WindowManager/Shell/AndroidManifest.xml
index bcb1d29..52ae93f 100644
--- a/libs/WindowManager/Shell/AndroidManifest.xml
+++ b/libs/WindowManager/Shell/AndroidManifest.xml
@@ -29,6 +29,7 @@
             android:name=".desktopmode.DesktopWallpaperActivity"
             android:excludeFromRecents="true"
             android:launchMode="singleInstance"
+            android:showForAllUsers="true"
             android:theme="@style/DesktopWallpaperTheme" />
 
         <activity