Verify the content length in the verity digest

When generating digest for verity, for the last incomplete 4k chunk, the
data is padded with 0s.  This implies that we can not tell from the
digest whether the file contains 0 or not, or how many 0s.

Since the verity hash is used by the kernel, the definition cannot be
change.  Instead, the actual hashed content length is appended to the
original digest and is verified before used.

Also uprev algorithm IDs.

Test: use new apksigner to sign an apk, apk can be installed on device
Bug: 30972906
Change-Id: I382af6e4090c7dc3f92d5acb5ac5d02d1f496992