Allow struct serialization from array input

[conr2d]

Change Description

eosio::chain::abi_serializer in libchain allows serialization of struct from array, but eosjs only serializes object to struct.

When sending a transaction with transaction_extensions, the abi of transaction in eosjs defines transaction_extensions as extension[], and extension is a struct with two fields, type (uint16) and data (bytes). However, during calling transact(), it calls /v1/chain/get_required_keys RPC, but in libchain, transaction_extensions is defined by std::vector<std::pair<uint16_t,vector<char>>>, so get_required_keys will be aborted, because libchain will fail to convert the parameters in json to eosio::chain::transaction.

At this time, there is no way to send a transaction with transaction extensions by transact() of eosjs-api. This PR will provide a way to serialize structs from array in the same manner as eosio::chain::abi_serializer and user experience of cleos. Moreover, user can send a transaction with transaction_extensions by setting them in array like:

const tx = {
  actions: [{
  ...
  }],
  transaction_extensions: [[1, [1]], [2, [1, 2, 3, 4]]]
};

API Changes

• [x] API Changes

User will be able to pass action parameters by array instead of object.

Documentation Additions

• [x] Documentation Additions

User can pass an array to transact() of eosjs-api.