Setup a common channel to trunk stable flags in system properties

This is a common root node for native trunk stable flags in system properties. Each flag in a namespace will appear in the sys prop as

persist.device_config.trunk_stable_flags.<namespace>.<flag>

Bug: b/295379636
Change-Id: I42e4a799781a9ced442cbdcbdb6b905446d72d73
diff --git a/private/system_server.te b/private/system_server.te
index dc6d322..2e1316d 100644
--- a/private/system_server.te
+++ b/private/system_server.te
@@ -766,6 +766,7 @@
 set_prop(system_server, device_config_configuration_prop)
 set_prop(system_server, device_config_connectivity_prop)
 set_prop(system_server, device_config_surface_flinger_native_boot_prop)
+set_prop(system_server, device_config_trunk_stable_flags_prop)
 set_prop(system_server, device_config_vendor_system_native_prop)
 set_prop(system_server, device_config_vendor_system_native_boot_prop)
 set_prop(system_server, device_config_virtualization_framework_native_prop)
@@ -1334,6 +1335,7 @@
   device_config_surface_flinger_native_boot_prop
   device_config_sys_traced_prop
   device_config_swcodec_native_prop
+  device_config_trunk_stable_flags_prop
   device_config_window_manager_native_boot_prop
 }:property_service set;