Add post_update.sh and regenerate .bp

* Regenerate .bp with new dependent package versions.
* Include out/version.rs in src/lib.rs.

Bug: 169119563
Test: tools/external_updater/updater.sh update rust/crates/protobuf
Test: mm in external/rust/crates/protobuf
Change-Id: I5df38edeaacb5ad83a46bb04b569f6935cf88df5
diff --git a/Android.bp b/Android.bp
index 0cd68bf..ad518d0 100644
--- a/Android.bp
+++ b/Android.bp
@@ -16,4 +16,4 @@
 }
 
 // dependent_library ["feature_list"]
-//   bytes-0.5.5 "default,std"
+//   bytes-0.5.6 "default,std"