Fix ClassMetadata type for SearchIndexMapping (#2988)

A `SearchIndexMapping` can have either `SearchIndexDefinition` or
`VectorSearchIndexDefinition` for `definition`. Currently it is missing
the latter.

Author: paulinevos

src/Mapping/ClassMetadata.php

@@ -269,7 +269,7 @@
  * @phpstan-type SearchIndexMapping array{
  *      type: "search"|"vectorSearch",
  *      name: string,
- *      definition: SearchIndexDefinition
+ *      definition: SearchIndexDefinition|VectorSearchIndexDefinition
  * }
  * @phpstan-type VectorSearchIndexField array{
  *     type: "vector"|"filter",