Vert.X: decrease the number of tokens created

[meiao]

Description

The Vert.X instrumentation will create a Token for each listener/handler added to its FutureImpl.
But when multiple listeners/handlers are added to the same FutureImpl, it creates a single ListenerArray, which could have a single Token instead.

Acceptance Criteria

When the ListenerArray is created, create a Token for it, but do not create any further Tokens for any new Listeners.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-351119