These doc updates were made previously to the java API but some
did not make it into the native API.
Change-Id: I9b7bfcd77bc593685254baca1c148deb7e1f91c7
related-to-bug: 8621588
Clarify offline usage of sessions and keys and implement
implement CryptoSession to support additional crypto use
cases.
Change-Id: I418ffbb37e3036a2b5eea5a86ac88a5af1a9da07