(REF) Extract compiler passes from CRM_Api4_Services

[totten]

Overview

CRM_Api4_Services has interesting behavior that (sort of) applies to all container-based services -- it detects services with the tags event_subscriber and spec_provider, and it registers them with the necessary provider (ie the event-dispatcher or the spec-gatherer).

This patch preserves support for these tags, but it moves the code to a more conventional spot, fixes a bug, and adds explanatory docblocks.

Before

It scans for tagged services (findTaggedServiceIds()) during the definition phase. This is too early. The tags will work for some services -- but they'll be quietly ignored on other services.

For example, if you define a tagged-service in Civi\Core\Container::createContainer(), then it will be recongized. But if you define the same tagged-service in hook_civicrm_container, then it won't be recognized.

After

It scans for tagged services (findTaggedServiceIds()) during the compilation process. This is slightly later -- after all service definitions have been defined.

Consequently, the tags will work the same way (regardless of who defines the service).

Technical Details

The key thing is to distinguish these use-cases:

• You may wish to define a service. This is generally done by calling $container->setDefinition() (et al).
• You may wish to define a generic handler to enhance other services. This is generally done by calling $container->addCompilerPass()

The prior code conflates these two things. The PR splits them apart (running as separate phases - in keeping with the general design of Symfony's ContainerBuilder).

Comments

The specific folders / interfaces / tags for CRM_Api4_Services may seem a bit alien. I submit that doesn't matter -- because there's a bunch of test-coverage that relies on CRM_Api4_Services(if it breaks, you'll see a lot of failures) and because it's a step toward #24276, which will allow a more consistent model.

[civibot]

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[colemanw]

Tests pass, so it works!