Move the app to /system_ext

We plan to forbid hidden API in product partition.
So these apps have to be moved to /system_ext because it uses hidden API.
It is not permanent, so they can be moved back to /product due to
needs if there isn't hidden usage anymore.

Bug: 137908189
Test: m
Test: check whether device boots successfully
Change-Id: I0662674a66bc54ee4713e5c7ed6ad0db4d342338
diff --git a/packages/WallpaperCropper/Android.bp b/packages/WallpaperCropper/Android.bp
index 40c4235..ac38b27 100644
--- a/packages/WallpaperCropper/Android.bp
+++ b/packages/WallpaperCropper/Android.bp
@@ -3,7 +3,7 @@
     srcs: ["src/**/*.java"],
     platform_apis: true,
     certificate: "platform",
-    product_specific: true,
+    system_ext_specific: true,
     privileged: true,
     optimize: {
         proguard_flags_files: ["proguard.flags"],