Added 'FieldClassifier' with nine F-row predicates and rewrote field-expansion pipeline.

[AlexSkrypnyk]

Summary

Introduces FieldClassifier and FieldClassifierInterface with nine F-row predicates (F1-F9) that classify every Drupal field by origin (base / configurable / bundle-storage-backed) and storage profile (standard / computed / custom). Core::expandEntityFields() is rewritten to route fields through the classifier — only F1 (base standard), F5 (configurable), and F9 (bundle-storage-backed) rows enter the handler pipeline, which eliminates the silent mis-classification of computed and non-writable base fields. DefaultHandler is tightened to throw a clear, actionable error for any field type whose schema is not single-column value, enforcing a loud-failure policy so broken handlers surface immediately. A full F-row truth table is documented in src/Drupal/Driver/Core/Field/README.md.

Stack

This PR is #2 of 4 in a stacked series:

• PR 1: feature/driver-interface → master (Tightened 'DrupalDriverInterface' contract and 'DrupalDriver' visibility. #358)
• PR 2 (this one): feature/field-classifier → feature/driver-interface
• PR 3: feature/field-coverage → feature/field-classifier
• PR 4: feature/ext-smoke-ci → feature/field-coverage

Merge in order. This PR depends on #358.

Changes

Field classifier

• Added FieldClassifierInterface with nine predicates: fieldIsBaseStandard, fieldIsBaseComputed, fieldIsBaseCustom, fieldIsConfigurableStandard, fieldIsConfigurableComputed, fieldIsConfigurableCustom, fieldIsBundleStorageBacked, fieldIsConfigurable, fieldIsBase.
• Added FieldClassifier implementing the interface, backed by EntityFieldManagerInterface.
• Core holds a lazily created FieldClassifierInterface instance exposed via classifier() on CoreInterface; subclasses override createFieldClassifier() to inject a version-specific implementation.

Pipeline rewrite

• Core::expandEntityFields() no longer accepts $base_fields; bundle is resolved automatically via resolveBundleFromEntity() (bundle key → step_bundle → entity type id).
• Core::getEntityFieldTypes() signature changed from array $base_fields = [] to ?string $bundle = NULL; the method now gates inclusion on classifier predicates (F1 OR F5 OR F9) rather than a hard-coded storage-config check.
• Core::expandEntityBaseFields() removed (was a thin wrapper; callers use expandEntityFields() directly).
• Core::detectBaseFieldsOnEntity() replaced by resolveBundleFromEntity().
• Core::fieldExists() and Core::fieldIsBase() removed; use classifier() predicates instead.
• Core::getFieldHandler() now passes the resolved bundle to getEntityFieldTypes().

DefaultHandler loud-failure policy

• DefaultHandler::expand() now throws \RuntimeException for any field whose storage schema is not a single value column, surfacing handler gaps immediately rather than silently returning garbage.

EntityReferenceRevisionsHandler

• Added handler for entity_reference_revisions fields (paragraphs, media, and other revision-tracked references); mirrors EntityReferenceHandler but targets target_revision_id alongside target_id.

Documentation

• Added src/Drupal/Driver/Core/Field/README.md with the F-row truth table, column definitions, and guidance on which rows enter the pipeline.
• UPGRADING.md updated with migration notes for removed predicates (fieldExists, fieldIsBase), the removed FieldCapabilityInterface, and the changed getEntityFieldTypes() signature.

Removed

• src/Drupal/Driver/Capability/FieldCapabilityInterface.php — contract superseded by classifier predicates.
• CoreInterface no longer extends FieldCapabilityInterface.
• DrupalDriverInterface no longer re-exports fieldExists / fieldIsBase.

Tests

• Added FieldClassifierTest (221 lines, unit, all nine predicates).
• Added EntityReferenceRevisionsHandlerTest (163 lines, unit).
• Expanded DefaultHandlerTest with loud-failure coverage.
• Added CoreEntityCreateModerationStateKernelTest — round-trip kernel test for F3 (writable computed base field moderation_state).
• Updated CoreFieldMethodsTest and CoreEntityMethodsKernelTest for the new signatures.

Before / After

BEFORE
------
expandEntityFields($type, $entity, $base_fields)
  getEntityFieldTypes($type, $base_fields)
    for each storage definition:
      if FieldStorageConfig  →  add (F5 only)
      if in $base_fields     →  add (any base field, no filter)
  for each field:
    handler->expand()        ← computed/non-writable fields slip through here

AFTER
-----
expandEntityFields($type, $entity)
  resolveBundleFromEntity()  →  bundle
  getEntityFieldTypes($type, bundle)
    for each definition (storage + base + bundle):
      classifier->fieldIsBaseStandard?      →  F1: add
      classifier->fieldIsConfigurable?      →  F5: add (scoped to bundle)
      classifier->fieldIsBundleStorageBacked? → F9: add
  for each field (id/bundle keys skipped):
    handler->expand()        ← only writable, handler-eligible fields reach here

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