keystore2: Use libbinder_rs Strong references for Binder objects

Update keystore2 to use libbinder_rs Strong<> and Weak<> references for
Binder objects rather than just Box<dyn Interface>.

Bug: 175584883
Test: atest keystore2_test
Change-Id: Ic234ce5ed007a265769a72043d77eb817a21b8ea
diff --git a/keystore2/src/utils.rs b/keystore2/src/utils.rs
index bada2c9..8e161b7 100644
--- a/keystore2/src/utils.rs
+++ b/keystore2/src/utils.rs
@@ -103,7 +103,7 @@
     }
 
     /// Clones the owned SpIBinder and attempts to convert it into the requested interface.
-    pub fn get_interface<T: FromIBinder + ?Sized>(&self) -> anyhow::Result<Box<T>> {
+    pub fn get_interface<T: FromIBinder + ?Sized>(&self) -> anyhow::Result<binder::Strong<T>> {
         // We can use unwrap here because we never panic when locked, so the mutex
         // can never be poisoned.
         let lock = self.0.lock().unwrap();