This change implements SipHasher in rust and java to make sure same
bytes array will be hashed into the same u64.
The implementation is needed, thus when rust, and java code read the
same flag file, they can find the same entry based on the same key.
Test: atest aconfig_storage_file.test.java aconfig_storage_file.test.cpp
Bug: 352078117
Change-Id: I2ce470039213a09a1df7637e60f4649b053fb2ea
