Provide the ability to instrument the queue system

Problem/Motivation

It's difficult for contrib or custom modules to instrument the queue system for performance monitoring purposes (or, to otherwise respond to jobs being queued or processed).

Steps to reproduce

Attempt to respond or "hook into" to queue operations, e.g. install modules/libraries that enable performance tracing and attempt to create performance tracing spans for queue operations.

Proposed resolution

Dispatch events for queue operations, e.g. ItemQueuing, ItemQueued, ItemProcessing, ItemExceptionOccurred, ItemProcessed.

Note, however, that queue processing may be re-implemented by Drush, contrib modules (e.g. ultimate_cron), etc. In the current architecture, each implementation would be responsible for correctly dispatching the events.

Remaining tasks

Review feature request and develop a merge request.

User interface changes

None.

Introduced terminology

None.

API changes

New events would be added to the queue API.

Data model changes

None.

Release notes snippet