This commit replaces the old implementation of `EMSA_PKCS1_V1_5` with
one backed by OpenSSL. In doing so, the `sign` and `verify` methods of
RSA have been modified to behave like expected and not just be
encryption and decryption.
I was not able to split this commit because the changes to `verify` and
`sign` break pretty much everything.
It used to be that the caller would supply a buffer to write the output
to. This created an anti-pattern in multiple places where the caller
would allocate a `ByteBuffer` and then use `.bytes()` to provide it to
the `PKSystem` method. Then the callee would resize the output buffer
and reassign it, but because the resize was on `Bytes` and not on
`ByteBuffer`, the caller using the latter would cause a bug.
Additionally, in pretty much all cases the buffer was pre-allocated
shortly before.
In order for public/private key serialization to work correctly we must
store the size of the key because P-521 cannot be stored as full words
inside `UnsignedBigInteger` and therefore is exported as the wrong
length (68 instead of 66).
This makes it also possible to refactor some methods and cleanup
constants scattered around.
Gets almost all import/export tests, expect the JWK ones that calculate
the public key on export. The `SECPxxxr1` implementation currently fails
to do calculations for P-521.
