The new chunked reader uses a Merkle tree to verify each chunk read of
the corresponding backing file. The reader also accepts an
autheneticator for signature verification, though it is currently a fake
implementation due to the lack of PKCS#7 signature support in BoringSSL
(b/170494765).
Test: atest authfs_host_test_src_lib
Bug: 171310075
Change-Id: Ibf4151ab2a93f7515ad8c9c0462df6c21c10d767
Victor Hsieh