Add fsverity digest manifest

fsverity digest manifest stores a map from files to fsverity digests.
The manifest is installed as a serialized protobuf file, to a signed apk
system/etc/security/fsverity/BuildManifest.apk.

Bug: 193113311
Test: build with PRODUCT_SYSTEM_FSVERITY_GENERATE_METADATA := true
Change-Id: I55fc10400206b8ce0d5f198faea08fe3930b362c
diff --git a/tools/releasetools/Android.bp b/tools/releasetools/Android.bp
index 4e628cf..a979a8e 100644
--- a/tools/releasetools/Android.bp
+++ b/tools/releasetools/Android.bp
@@ -265,8 +265,8 @@
     srcs: [
         "fsverity_metadata_generator.py",
     ],
-    required: [
-        "fsverity",
+    libs: [
+        "fsverity_digests_proto_python",
     ],
 }