Currently, when the SSLEngine needs to produce handshake or close data,
we must manually call the nonApplicationWrite method. However, this data
is only required when something triggers the need (starting handshake,
reading from the wire, initiating close, etc). As we have a dedicated
outbound buffer, this data can be produced automatically. Additionally,
with this refactoring, we combine handshake and application mode into a
single mode. This is necessary as there are non-application messages that
are sent post handshake in TLS 1.3. Finally, this commit modifies the
SSLDriver tests to test against TLS 1.3.
667c613d9e