Support handling build releases in sdk snapshot

Adds the following:
1. A buildRelease type to represent a single build release.
2. A buildReleaseSet type to represent a set of build releases.
3. Methods to create parse and use the previous new types.
4. Tests for the above.

Bug: 197842263
Test: m nothing
Change-Id: Ib0dd4fc32851a4fffde3fa02ea22c8369f8c2995