Add UnstructuredParcelable trait and macros.

Bug: 303064346
Test: atest aidl_integration_test
Change-Id: I067e05d5f03b678c963ac159574116ef3e33c9ed
diff --git a/libs/binder/rust/src/parcel.rs b/libs/binder/rust/src/parcel.rs
index f9f135d..3bfc425 100644
--- a/libs/binder/rust/src/parcel.rs
+++ b/libs/binder/rust/src/parcel.rs
@@ -34,7 +34,7 @@
 pub use self::file_descriptor::ParcelFileDescriptor;
 pub use self::parcelable::{
     Deserialize, DeserializeArray, DeserializeOption, Parcelable, Serialize, SerializeArray,
-    SerializeOption, NON_NULL_PARCELABLE_FLAG, NULL_PARCELABLE_FLAG,
+    SerializeOption, UnstructuredParcelable, NON_NULL_PARCELABLE_FLAG, NULL_PARCELABLE_FLAG,
 };
 pub use self::parcelable_holder::{ParcelableHolder, ParcelableMetadata};