MINOR: quic: Implement quic_tls_derive_token_secret().

MINOR: quic: Implement quic_tls_derive_token_secret().

This is function is similar to quic_tls_derive_retry_token_secret().
Its aim is to derive the secret used to cipher the token to be used
for future connections.

This patch renames quic_tls_derive_retry_token_secret() to a more
and reuses its code to produce a more generic one: quic_do_tls_derive_token_secret().
Two arguments are added to this latter to produce both quic_tls_derive_retry_token_secret()
and quic_tls_derive_token_secret() new function which calls
quic_do_tls_derive_token_secret().