This commit introduces a WEB_SET_PROTOTYPE_FOR_INTERFACE macro that
caches the interface name in a local static FlyString. This means that
we only pay for FlyString-from-literal lookup once per browser lifetime
instead of every time the interface is instantiated.
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.
