Keystore 2.0: Add safe crypto wrapper

 * Adds safe wrappers for AES_gcm_decrypt and AES_gcm_encrypt.
 * Adds AES256 key generation.
 * Adds ZVec, a simple fixed size owned vector type that locks
   the backing memory in place with mlock and zeroes the buffer
   before freeing it.

Test: keystore2_test
Bug: 173545997
Change-Id: Id7e30d50b024da1fa8aa58a07cd9bb7a861f81f0
7 files changed