Provide vert.x executor adapter which implements ScheduledExecutorService

#### Describe the feature

Vert.x executor has a number of very useful features, notably the ability to detect and address locked threads.
Providing a standard interface for this executor will immensely enhance its utility.

#### Use cases

e.g. that will add compatibility with Guava ListenableFutures, and all other libraries that use standard java executor.

#### Contribution

For now I'll just leave this proposal here.