Add system captions manager service

This service connects to a remote system captions manager service. This
service is responsible for enabling system captions when the user
requests them. As the system binds to it, this service will be
persistent.

Bug: 128925852
Test: Manual. I created an implementation of the service.
Change-Id: Iafde1bb68f4754d8167624f47c6833d43c0ec336
diff --git a/services/Android.bp b/services/Android.bp
index 567efac..b08d1a8 100644
--- a/services/Android.bp
+++ b/services/Android.bp
@@ -31,6 +31,7 @@
         "services.print",
         "services.restrictions",
         "services.startop",
+        "services.systemcaptions",
         "services.usage",
         "services.usb",
         "services.voiceinteraction",