Minimal approach to remove metastore_resource_mapper_new_revision

[dafeder]

This is a more minimal approach to #4750. Also copilot-generated, please ignore until I've come back to this, just bookmarking an experiment while I go back to other things.

Need to look at this carefully, I really don't remember exactly why we needed this originally; where the thread was getting lost in the workflow.

Copilot's explanation of changes:

Implemented an incremental transition path that runs both mechanisms in parallel: explicit decision propagation is now supported, while the legacy static flag remains the fallback and source of backward compatibility.

Changed files:

• DatastoreSubscriber.php
• LifeCycle.php
• Referencer.php

What this incremental path looks like:

1. Subscriber computes decision once, publishes it two ways.

• In DatastoreSubscriber.php, onPreReference now:
• Accepts both payload shapes:
  • legacy event data: MetastoreItemInterface
  • new payload object: { item, createNewResourceVersion }
• Computes should_create_new_resource_version as before.
• Writes legacy static flag (metastore_resource_mapper_new_revision) for existing callers.
• Also writes explicit createNewResourceVersion onto event payload for new callers.

2. Lifecycle now sends/reads explicit payload but does not require it.

• In LifeCycle.php, referenceMetadata now:
• Dispatches pre-reference event with payload object containing item and nullable createNewResourceVersion.
• Reads back createNewResourceVersion if subscriber sets it.
• Passes nullable decision into referencer.

3. Referencer accepts explicit decision with legacy fallback.

• In Referencer.php:
• Added optional ?bool $createNewResourceVersion = NULL through reference, referenceProperty, referenceMultiple, referenceSingle, distributionHandling, registerWithResourceMapper, and handleExistingResource.
• If explicit decision is NULL, handleExistingResource falls back to ResourceMapper::newRevision() exactly as before.
• If explicit decision is set, it takes precedence.

Validation run:

• ddev phpunit DatastoreSubscriberTest.php --stop-on-error passed.
• ddev phpunit ReferencerTest.php --stop-on-error passed.
• ddev phpunit OnPreReferenceTest.php --stop-on-error passed.

This gives you a safe bridge state:

• Old behavior still works unchanged.
• New explicit-parameter flow is live and can be expanded.
• Final cleanup later can remove static usage once all callers are explicit.

If you want, next I can do the follow-up phase that removes the static fallback from Referencer.php only after adding one targeted test that proves explicit-only behavior.

Completed: Fix subscriber unit tests for constructor signature change (1/4)

Made changes.