[IndexedDB] Standardize key-or-keyrange argument handling (#12)

The spec words this in various ways, and sometimes passes a key-or-keyrange to operations. This should be made consistent - operations should take a range, conversion should use the same substeps, and (ideally) we'd make this a spec "macro"

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/IndexedDB/issues/12