Move SystemUI to /system_ext

we plan to forbid hidden API in product partition.
So this app should 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
Test: atest SystemUITests
Change-Id: I54f86496d4a0045af3576091cce00e5cd285b4f8
diff --git a/packages/CarSystemUI/Android.bp b/packages/CarSystemUI/Android.bp
index b2451c9..56f5a96 100644
--- a/packages/CarSystemUI/Android.bp
+++ b/packages/CarSystemUI/Android.bp
@@ -140,7 +140,7 @@
     ],
 
     platform_apis: true,
-    product_specific: true,
+    system_ext_specific: true,
     certificate: "platform",
     privileged: true,