See http://b/issue?id=1751571
Changes the semantics of SmsHeader from containing only opaque data
to exposing occurs-once frequently-used fields together with a list
of opaque fields. Also changes the coding to and from byte array to
be symmetrical, whereas previous encoding had an extra length field.
Cdma SmsMessage -- cleanup of code paths along with adjustments to
match the new header semantics, which should address at least some
of the issues with concatenated messages. See http://b/issue?id=1809759
