Moves first parts of backup crypto code (ChunkHash class) to the framework.

Some changes were needed to the original code:
- Guava's EqualsTester tests are replaced by regular equals tests.
- Guava's primitives.UnsignedBytes.LexicographicalComparator needed to
be copied over, as no corresponding comparator exists in the framework.

Bug: 111386661
Test: atest RunFrameworksServicesRoboTests
Change-Id: I24fef4b47f7777b9be0c2e51f0be48e45b323987