Move VM callback to vmclient

Instead of having clients directly register a callback with VS,
implement a Rust level callback interface in vmclient. This saves an
extra binder call on each notification, a bunch of boilerplate code,
and allows us to provide a slightly better interface (e.g. we can use
the Rust DeathReason enum, as elsewhere in vmclient, for instantly
better logging).

I also replaced all our usages of <some_interface>::binder::{...} with
direct access to binder::{...}. That makes it clearer what depends on
the interface itself and what is just generic binder code. I realise
this should be a separate change, but I only realised that after doing
bits of both.

Test: composd_cmd test-compile, observe logs (on both success & failure)
Test: atest -b (to make sure all our tests build)
Test: Presubmits
Change-Id: Iceda8d7b8f8008f9d7a2c51106c2794f09bb378e
diff --git a/compos/composd/src/composd_main.rs b/compos/composd/src/composd_main.rs
index ebcd689..5315828 100644
--- a/compos/composd/src/composd_main.rs
+++ b/compos/composd/src/composd_main.rs
@@ -25,8 +25,8 @@
 mod service;
 
 use crate::instance_manager::InstanceManager;
-use android_system_composd::binder::{register_lazy_service, ProcessState};
 use anyhow::{Context, Result};
+use binder::{register_lazy_service, ProcessState};
 use log::{error, info};
 use std::panic;
 use std::sync::Arc;