Without this interface, index related operations cannot be implemented (for example IDBObjectStore::getKey).

Spec link: https://w3c.github.io/IndexedDB/#index-interface

• Stub interface Stub out IDBIndex #38813
• Implement creating/deleting indices (sync operations that are somewhat separate from the rest of the API) indexeddb: IDBIndex creation and deletion #38840
• Create schemas for storing index data indexeddb: Add index schemas #38891
• Update index data during each put, clear, and delete operation. indexeddb: Update index data in backend #42416
• Implement IDBIndex interface. (Partially by indexeddb: Update index data in backend #42416, more has to be done though)
• Implement cursors for iterating through indices See also: Implement IndexedDB cursors #38111