WebAuthN Support

[b1bart]

Change Description

Added support for WebAuthN keys and signatures to the c++ wrapper types. Deprecated the fixed size capi_ types for both signature and public_key as they are no longer sufficient to represent the potentially variable-sized keys in the future

API Changes

• API Changes
  The c++ types for eosio::signature and eosio::public_key are different. Before these were simple structs with public fields for the "which" type of public key and underlying buffer of bytes, these are now variants of either an std::array<char, 65> or a webauthn_signature and std::array<char, 33> or a webauthn_public_key respectively.

Documentation Additions

• Documentation Additions

The c++ types for eosio::signature and eosio::public_key have become significantly more complex to handle the unexposed details of what those data types really were. This resulted in shifting the types to std::variant and creating (sometimes shared) sub-types to represent the underlying types. Need to review the docs to make sure its reasonably legible.

[boid-com]

Is this change to eosio::public_key properly documented?

All official documentation points to cdt 1.5
https://developers.eos.io/manuals/eosio.cdt/v1.5/structeosio_1_1public__key

cdt 1.7 does not contain eosio::public_key documentation

[iamveritas]

public_key is now an alias not a struct anymore and, although it is annotated properly, in doxygen style, the documentation generation platform is not parsing it.