[IndexedDB] Support binary keys (#21)

Migrated from https://www.w3.org/Bugs/Public/show_bug.cgi?id=23332

* Align with WebIDL guidance:
  * Input is what WebIDL calls `BufferSource` - an `ArrayBuffer` or view
  * Output is an `ArrayBuffer`
* Sort as unsigned octets (i.e. new ArrayBuffer([255]) > ArrayBuffer([0])
* Binary keys sort higher than strings, lower than arrays


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Reply to this email directly or view it on GitHub:
https://github.com/w3c/IndexedDB/issues/21