[webidl] Distinguishability of buffers source types needs to be defined better (#50)

Right now the spec says that "buffer source types" are not distinguishable from each other.  But this is clearly wrong, since if that were the case the `BufferSource` typedef would not be valid.

I believe the right behavior here is that `ArrayBuffer` is distinguishable from everything that's not `ArrayBuffer`, `ArrayBufferView` is distinguishable from everything that's not `ArrayBufferView` or a typed array type, and a typed array type is distinguishable from everything except `ArrayBufferView` and itself.

I'm not sure how best to put this in the form of this table, because it would make the table huge...

Perhaps the simplest thing to do is to define that distinguishability works as if these were all interface types with the typed array interfaces considered as inheriting the `ArrayBufferView` interface.

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Reply to this email directly or view it on GitHub:
https://github.com/heycam/webidl/issues/50