transcoding: move transcoding service to apex

And conditionally start transcoding service

bug: 159172726
Change-Id: I13d126f342d4ea944d1e9186b4edcdfe5fb4b0a0
diff --git a/media/mediaserver/mediaserver.rc b/media/mediaserver/mediaserver.rc
index 05373c9..c82e532 100644
--- a/media/mediaserver/mediaserver.rc
+++ b/media/mediaserver/mediaserver.rc
@@ -7,3 +7,9 @@
     group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
     ioprio rt 4
     task_profiles ProcessCapacityHigh HighPerformance
+
+# media.transcoding service is defined on com.android.media apex which goes back
+# to API29, but we only want it started on API31+ devices. So we declare it as
+# "disabled" and start it explicitly on boot.
+on boot
+    start media.transcoding