Consider whether the others Public Value input to (EC)DH deriveKey should be a Key object

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24830

Presently, if the other's public value for the two DH algorithms is
received in spki format, then it is necessary first to import this
structure to obtain a Key object and then to export that in raw format
to obtain an ArrayBuffer containing the Public Value. This may then be
used with deriveKey.

If this is the more common use-case it would make sense to change the
type of the public property of (Ec)DhDeriveParams to have type Key.

If we make that change, then the other use-case where the Public Value
is received in some other form and extracted to an ArrayBuffer by the
application would require that ArrayBuffer to be imported to obtain a
Key. Thus the steps would be the same in both cases: import the
received public value, provide this Key object to deriveKey.


...Mark