Rather than trying to store a Handle to a WebIDL::BufferSource, let's
look ahead to what the spec wants us to do with this field and get a
copy of the bytes held by the buffer source right away.
This patch implements and tests window.crypto.sublte.generateKey with
an RSA-OAEP algorithm. In order for the types to be happy, the
KeyAlgorithms objects are moved to their own .h/.cpp pair, and the new
KeyAlgorithms for RSA are added there.
This patch throws away some of the spec suggestions for how to implement
the normalize_algorithm AO and uses a new pattern that we can actually
extend in our C++.
Also update CryptoKey to store the key data.
