[PHP Worker] listen to all PHP instances events via worker.addEventListener() - #2673

…stener()

Before this PR, worker.addEventListener() only listens to the events
emitted by the primary PHP instance. After this PR, it listens to events
emitted by all the PHP instances created by a given worker.

 ## Implementation details

Instead of passing through the `worker.addEventListener()` call to the
primary PHP instance, the PHPWorker class:

* Registers a wildcard event listener for all PHP events.
* Maintains its own list of event listeners.

Whenever any PHP instance emits an event that has worker-wide listeners
registered, the worker class notifies them.

This PR refactors all the worker implementations: web and node, v1 and
v2.

 ## Testing instructions

CI (TODO: Add test coverage)