SearchIndex: rector, phpcs, type hint fixes

SearchIndex: rewrite Indexer to use Collection classes

Replace the intermediate #2943 classes (FulltextIndex, MetadataIndex)
with the new Collection-based architecture. The Indexer is now a thin
sta

SearchIndex: rewrite Indexer to use Collection classes

Replace the intermediate #2943 classes (FulltextIndex, MetadataIndex)
with the new Collection-based architecture. The Indexer is now a thin
stateless orchestrator that delegates all index work to collections.

Key changes:
- Indexer no longer extends AbstractIndex; page name passed to methods
- addPage/deletePage/clear use PageTitleCollection,
PageFulltextCollection, and PageMetaCollection
- New PageMetaCollection replaces separate ReferencesCollection and
MediaCollection with a single class that handles arbitrary metadata
keys dynamically
- Shared writable FileIndex('page') passed to all collections
- Logger callback replaces verbose parameter
- Methods return void instead of bool
- Index classes implement IteratorAggregate for clean data access
- Indexer tests consolidated into namespaced IndexerTest.php
- All callers updated to new stateless API

show more ...