Add microbenchmarks for KeyAgreement and Cipher algorithms. Measuring KeyAgreement is very useful, because it reveals the performance of general EC point arithmetic. The ECC algorithms in KeyPairGenerator and Signature require only base point arithmetic, which can be done more efficiently. There are existing benchmarks for some variants of AES, but not a general-purpose Cipher benchmark. The new benchmark will allow us to measure non-AES ciphers such as ChaCha20.