Fixes#5996
* Add extensions to probe message for EC, others
probeMFLN was failing on some connection attempts to servers which only
supported EC based ciphers because it did not include the proper TLS
handshake extensions to list what kinds of ECs it supported.
Add those to the probeMFLN ClientHello message to make probes pass.
* Add client.getMFLNStatus method, returns MFLN state
After a connection it is useful to check whether MFLN negotiation
succeeded. getMFLNStatus returns a bool (valid only after
client.connect() succeeds, of course) indicating whether the requested
buffer sizes were negotiated successfully.
BearSSLX509List, BearSSLSession, BearSSLPublicKey, and BearSSLPrivateKey
were all in the global namespace and not in the BearSSL:: one, due to an
oversight when they were originally created. Move them to the proper
namespace with the following mapping:
BearSSLX509List => BearSSL::X509List
BearSSLSession => BearSSL::Session
BearSSLPublicKey => BearSSL::PublicKey
BearSSLPrivateKey => BearSSL::PrivateKey
