[IndexedDB] Standardize relationship between concept-objects and interface-objects (#10)

The relationship between e.g. __cursor__ and `IDBCursor` is not described consistently. Modern specs (e.g. fetch) formally define the relationship as a script-object `IDBCursor` having an associated concept-object. This spec just says things like __cursor__ implements `IDBCursor`, and method definitions implicitly have a "this __cursor__..." in scope.

The most extreme case of this is detailed in #3 (where __object store__ and `IDBObjectStore` don't have a 1:1 mapping).

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/IndexedDB/issues/10