Make the protected fields in AbstractJackson2Encoder private plus
minor refactoring to the way streaming separators are applied.
The current (5.0.3) behavior is to always use '\n', but in 5.0.4 the
newly supported "application/stream+x-jackson-smile" needs to be
excluded from that. For now, separator determination remains private
in the abstract base class, but current behavior remains which is to
apply '\n' by default.
Issue: SPR-15424
0ead0503eb