Implement Send trait for Binder<T>

Binder objects need to be Send for AIDL services which have a Binder
service in the response message.

Bug: 161559357
Test: atest rustBinderTest
Change-Id: I68f4219756a566fa9e8b48bbda8e292cd164de26
diff --git a/libs/binder/rust/src/binder.rs b/libs/binder/rust/src/binder.rs
index f5e7509..d55eafe 100644
--- a/libs/binder/rust/src/binder.rs
+++ b/libs/binder/rust/src/binder.rs
@@ -61,7 +61,7 @@
 /// the AIDL backend, users need only implement the high-level AIDL-defined
 /// interface. The AIDL compiler then generates a container struct that wraps
 /// the user-defined service and implements `Remotable`.
-pub trait Remotable: Sync {
+pub trait Remotable: Send + Sync {
     /// The Binder interface descriptor string.
     ///
     /// This string is a unique identifier for a Binder interface, and should be