Use fs-verity digests proto to build the directory

The proto contains path -> digest mapping. In this change, we start to
use the provided protobuf to build the directory. Digest is not yet
used.

Bug: 206869687
Test: atest AuthFsHostTest ComposHostTestCases MicrodroidTestCase
Change-Id: I0f03219c1243f20f9ec5099a451c6f588add9608
diff --git a/authfs/Android.bp b/authfs/Android.bp
index 471b0cf..ef78d4e 100644
--- a/authfs/Android.bp
+++ b/authfs/Android.bp
@@ -18,10 +18,12 @@
         "libbinder_rpc_unstable_bindgen",
         "libbinder_rs",
         "libcfg_if",
+        "libfsverity_digests_proto_rust",
         "libfuse_rust",
         "liblibc",
         "liblog_rust",
         "libnix",
+        "libprotobuf",
         "libstructopt",
         "libthiserror",
     ],