Replicate what we are doing with RSA and parse both the private and
public key when parsing the ASN1.
The only thing that changed in the tests is the error message.
I have divided ANS1 constants by length so that they don't have
trailing zeros that need to be removed.
Also moved OIDs lists to the only place they are used for clarity.
Fixed a couple of WPT tests by adding SECP521r1 to the list of known
curves.
Parse and store the `ECPrivateKey` extracted from the
`privateKeyAlgorithm` field of the ASN.1 `PrivateKeyInfo` sequence when
the algorithm identifier is `ec_public_key_encryption`.
The parsing function returns `ErrorOr` instead of an "empty" key, like
`parse_rsa_key` does. To me, this seemed better in terms of reliability.
As mentioned in the previous commit, there is room for improvement.
By moving `Certificate` to `LibCrypto` it is possible to reuse a bunch
of code from in `LibCrypto` itself. It also moves some constants
and pieces of code to a more appropriate place than `LibTLS`.
This also makes future work on WebCryptoAPI easier.
