Allow grilservice apps to access app_api_service

Sync solution from ag/12369854 which allow grilservice_app to use
app_api_service.
The tethering_service is one kind of app_api_service.
The activity_service is also one kind of app_api_service.

avc:  denied  { find } for pid=3531 uid=10118 name=tethering scontext=u:r:grilservice_app:s0:c118,c256,c512,c768 tcontext=u:object_r:tethering_service:s0 tclass=service_manager permissive=0

Bug: 169389307
Test: the device can boot to home. check if avc denied from grilservice_app.
Merged-In: I9496323003b19ab97fc2c330ea4dc9b7d5d4dd60
Change-Id: I6da3169c6ee4f847e56eb07223cfdde46e885fe1

diff --git a/vendor/google/grilservice_app.te b/vendor/google/grilservice_app.te
index a1adeab..68667c4 100644
--- a/vendor/google/grilservice_app.te
+++ b/vendor/google/grilservice_app.te

@@ -4,7 +4,7 @@
 
 allow grilservice_app hal_radioext_hwservice:hwservice_manager find;
 allow grilservice_app hal_wifi_ext_hwservice:hwservice_manager find;
-allow grilservice_app activity_service:service_manager find;
+allow grilservice_app app_api_service:service_manager find;
 
 binder_call(grilservice_app, hal_radioext_default)
 binder_call(grilservice_app, hal_wifi_ext)