Implement structs and enums from type: contract Fuel spec

[QuinnLee]

Currently, function is only one supported.

With more custom data types, abi of type contract with struct definitions will be added. https://github.com/FuelLabs/fuel-specs/blob/master/specs/protocol/abi.md#json-abi-format

Implement contract type

[luizstacio]

Doing swayswap-demo has been a pain point as the returns are not strong typed but instead returning a any type. It's true for ContractId, Address, and custom structures.

Use case;

Contract ABI

fn withdraw(amount: u64, asset_id: ContractId);

Types definition from the typechain

withdraw(
      amount: BigNumberish,
      asset_id: any,
      overrides?: Overrides & { from?: string | Promise<string> }
): Promise<any>;

Typescript implementation

const return = await swayswap.functions.just_return(1, {
      value: REACT_APP_TOKEN_ID
});