CipherSpi for HPKE

[ocadaruma]

Hi, folks!

Currently, bc-java doesn't have CipherSpi for HPKE, while some hybrid encryption schemes have (e.g. ECIES).
HPKE implementation itself is there, but it only exposes low-level HPKE functions so it's not convenient to use.

I imagine an API like:

Cipher cipher = Cipher.getInstance("HPKE");
cipher.init(new HPKEParameterSpec(...));

What do you think about this?

Thanks!