Split compos_key_service.

Split the code that implements the service from the code that starts
it as a binder service. This is preparation for also allowing it to be
started in a VM.

Bug: 193603140
Test: Run compos_key_host, connect to it via compos_key_cmd
Change-Id: I8f223ef19c9490dc349e1f677f670eedcf09dead
diff --git a/compos/apex/Android.bp b/compos/apex/Android.bp
index 2dded99..c4ab321 100644
--- a/compos/apex/Android.bp
+++ b/compos/apex/Android.bp
@@ -38,7 +38,7 @@
 
     binaries: [
         "compos_key_cmd",
-        "compos_key_service",
+        "compos_key_host",
         "compsvc",
         "compsvc_worker",
         "pvm_exec",