Split compsvc.rs.

Separate out the implementation of the service from the main program
that makes it available on the appropriate binder.

This is inteded as a pure refactoring, preparatory to hosting both
compsvc and CompOsKeyService in a single binary.

Bug: 194267113
Test: atest ComposHostTestCases (with testOdrefesh un-ignored)
Change-Id: I0c3015f1b962bf895dd93b9f6eb74b4e55a85c9e
diff --git a/compos/Android.bp b/compos/Android.bp
index 9428210..ad99d51 100644
--- a/compos/Android.bp
+++ b/compos/Android.bp
@@ -28,7 +28,7 @@
 
 rust_binary {
     name: "compsvc",
-    srcs: ["src/compsvc.rs"],
+    srcs: ["src/compsvc_main.rs"],
     rustlibs: [
         "compos_aidl_interface-rust",
         "libandroid_logger",