Add proptools.Hash type as return type of proptools.CalculateHash

A uint64 may prove to be too small of a hash, change the return type
of proptools.CalculateHash to a new Hash type whose size can be
changed later if necessary.

Test: hash_provider_test.go
Change-Id: Ib9a7ff7a22901f8b40f0edb20a21abc70277685b
11 files changed