It is helpful to be able to run apps concurrently written
in successive versions of Rails to aid migration, e.g. run
Rails 4.2 and 5.0 variants of your application at the same
time to carry out A/B testing.

To do this serialization formats need to be cross compatible
and the change in 3aa26cfb didn't meet this criteria because
the Psych loader checks for the existence of init_with before
setting the instance variables and the wrapping behavior of
ActiveSupport::TimeWithZone tries to see if the Time instance
responds to init_with before the @time variable is set.

To fix this we backported just the init_with behavior from
the change in 3aa26cfb. If the revived instance is then
written out to YAML again it will revert to the default
Rails 4.2 behavior of converting it to a UTC timestamp string.

Fixes #26296.