updateIndex() drops collection and loses all indexed documents on config import

Steps to reproduce

1. Have a Typesense collection with indexed documents (e.g., 80k+ products)
2. Add a new field to the Search API index configuration (search_api.index.*.yml)
3. Run drush cim or drush deploy
4. Observe that Typesense collection is empty - all documents are lost

Root cause: SearchApiTypesenseBackend::updateIndex() calls removeIndex() which drops the entire collection. The exportCollectionData() method only exports synonyms/curations, NOT the actual documents.

Proposed resolution

Use Typesense's PATCH API to update schema without dropping the collection.

The patch:

• Adds updateCollectionSchema() method to TypesenseClient using PATCH API
• Modifies updateIndex() to compare schemas and only add/remove changed fields
• Preserves all existing documents
• Only triggers reindex() when new fields are added (to populate their data)
• Re-throws exceptions instead of silently logging them

See: Typesense PATCH API docs

Remaining tasks

• Review patch
• Test with different field types
• Commit

User interface changes

None.

API changes

New method added to TypesenseClientInterface:

public function updateCollectionSchema(string $collection_name, array $fields_to_add, array $fields_to_drop): void;

Data model changes

None.