Take special care of aggressive elision in certain tagged elements

[volrath]

Some tagged elements, like unrepl/object, have data structures as their "element", and in this cases, we want to make sure these data structures are not elided when :nesting-depth is reached.

Example:

[:eval
 #unrepl/object [#unrepl.java/class datomic.promise$settable_future$reify__7020
                 "0x735919a8"
                 {:unrepl.ref/status :ready,
                  :unrepl.ref/val {:db-before #datomic.db.Db {:id "datomic:dev://localhost:2718/ng",
                                                              :memidx #datomic.db.IndexSet {:eavt #{#unrepl/object [#unrepl/... {:get (unrepl.replG__8056/fetch :G__8575)}]
 ;; etc...
 5]

In this snippet, the most nested element is a tagged #unrepl/object, which is represented by a vector and it's elided.

a4bfbfe is a step towards solving this.