Timeline for upgrading `jackson-databind` to require Java 8

[Tatu Saloranta]

Ok, time to bring this up again.

So. Currently jackson-databind 2.10 may be run on JDK 7 (*). Other
components differ in that jackson-annotations and jackson-core run on
JDK 6, and some modules need JDK8 (Java 8 obviously, but some
dataformats have deps that need Java 8 as well).

Jackson 3.0 (master) requires JDK 8 already; but since it is in
development, target JDK can be re-considered at some point.

But. Would it make sense to upgrade baseline JDK 8 requirement for
`jackson-databind`? Doing this would mostly matter (IMO) in that doing
that would allow use of closures (method pointers) for API /
configuration. There would be some other smaller benefits, like
directly including `Optional` support, constructor name parameter
access.

If we were to move the baseline, this could happen as early as 2.11
(probably due in Jan 2020), or if not, following that in 2.12.
Whatever version predating this version would also become "long-term
supported" Jackson version, i.e. be patched longer than usual, to
support use cases where going Java 8 is not possible

But first I would like to know of users, if any, that use Jackson on
pre-Java8 platforms (or platforms where full JDK 8 based version would
not work).

So: concerns, comments, suggestions?

-+ Tatu +-

(*) there are occasionally reported issues wrt whether it truly works
on some of sorta-J2SE platforms, like Android, but aside from those