Add methods to get locked buffer from Surface.

Bug: 307535208
Test: atest libnativewindow_rs-internal_test
Change-Id: Ib9a824a72d1d415dddd82e477d55200765d0b9e6
diff --git a/libs/nativewindow/rust/src/lib.rs b/libs/nativewindow/rust/src/lib.rs
index 931c311..f19b908 100644
--- a/libs/nativewindow/rust/src/lib.rs
+++ b/libs/nativewindow/rust/src/lib.rs
@@ -19,10 +19,9 @@
 mod handle;
 mod surface;
 
-pub use handle::NativeHandle;
-pub use surface::Surface;
-
 pub use ffi::{AHardwareBuffer_Format, AHardwareBuffer_UsageFlags};
+pub use handle::NativeHandle;
+pub use surface::{buffer::Buffer, Surface};
 
 use binder::{
     binder_impl::{BorrowedParcel, UnstructuredParcelable},