Also renamed releaseResources->release to be consistent with the
rest of the library, and added some synchronization to ensure
correct usage.
Issue: #2139
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150753414
1. Move entire library from v2/library/ to v2/library/core
2. Add v2/library/all that depends on v2/library/core
Issue: #2139
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150455693