system_server: create StatsManagerService

Refactor to split the logic within statscompanion_service
The goal of the refactor is to simplify the binder calls to statsd

This service will talk to statsd.

At the end of the refactor, this service should be the only
service that talks to statsd.

Bug: 146074223
Test: Manual by creating the service with empty implementation
Change-Id: Ib9c2e10ec195d41062f1001e5a82b374696de939
diff --git a/private/service_contexts b/private/service_contexts
index 7540705..2fe622d 100644
--- a/private/service_contexts
+++ b/private/service_contexts
@@ -188,6 +188,7 @@
 slice                                     u:object_r:slice_service:s0
 stats                                     u:object_r:stats_service:s0
 statscompanion                            u:object_r:statscompanion_service:s0
+statsmanager                              u:object_r:statsmanager_service:s0
 soundtrigger                              u:object_r:voiceinteraction_service:s0
 soundtrigger_middleware                   u:object_r:soundtrigger_middleware_service:s0
 statusbar                                 u:object_r:statusbar_service:s0