Initial sepolicy for composd

Add what we need to allow composd to run and expose an AIDL service.

Also delete the policy for compsvc; we never access it in the host
now, and the real policy is in microdroid. Retain the compos_exec
type, since it is referenced in the APEX sepolicy.

Bug: 186126194
Test: adb shell cmd -w android.system.composd; no denials.
Change-Id: I5f06b2b01852cdebd2d67009b363ec08b17ce33a
diff --git a/apex/com.android.compos-file_contexts b/apex/com.android.compos-file_contexts
index ecec6b5..0502084 100644
--- a/apex/com.android.compos-file_contexts
+++ b/apex/com.android.compos-file_contexts
@@ -1,3 +1,4 @@
 (/.*)?                   u:object_r:system_file:s0
 /bin/compsvc             u:object_r:compos_exec:s0
 /bin/compos_verify_key   u:object_r:compos_verify_key_exec:s0
+/bin/composd             u:object_r:composd_exec:s0