Generate Rust binding for fsverity_digests.proto

Bug: 206869687
Test: Can use it from authfs
Change-Id: I1bc78dcbf89c210e4648bebc68bd6631351d29cd
diff --git a/fsverity/Android.bp b/fsverity/Android.bp
index 5fb38ae..5c3d6a0 100644
--- a/fsverity/Android.bp
+++ b/fsverity/Android.bp
@@ -41,3 +41,15 @@
         },
     },
 }
+
+rust_protobuf {
+    name: "libfsverity_digests_proto_rust",
+    crate_name: "fsverity_digests_proto",
+    source_stem: "fsverity_digests_proto",
+    protos: [
+        "fsverity_digests.proto",
+    ],
+    apex_available: [
+        "com.android.compos",
+    ],
+}