Experiment to improve E2E call builder API

[ascjones]

Playing around to see how we can simply remove the existing ugly callback API for building message calls. The requirements are:

1. Absolutely changes and no breaking changes to the ink call builder codegen.
2. Nice and clean API.

With this idea I have converted erc20 to the new syntax which removes the unergonomic callback. Thus we can now use call on the type returned from instantiate:

// instantiate
let mut erc20 = client
    .instantiate::<Erc20, _, _>(
        "erc20",
        &ink_e2e::bob(),
        constructor,
        0,
        None,
    )
    .await
    .expect("instantiate failed");

// build the call (no longer requires callback)
let transfer_from = erc20.call().transfer_from(
    bob_account.clone(),
    charlie_account.clone(),
    500_000_000u128,
);

/// invoke the call
client
  .call(&ink_e2e::charlie(), &transfer_from, 0, None)
  .await

To test this run e2e tests on the erc20 example.

Things to see whether we improve

• remove requirement for explicit type hint on instantiate, see .instantiate::<Erc20, _, _> above
• can we get around the requirement for mutable let mut contract ref to access messages with &mut self receivers.
• can we avoid the addidional Clone impls added to the call builders (required because many call builder methods consume self)

[ascjones]

@SkymanOne let me know if this PR is helpful or not, otherwise I can just close it.

[SkymanOne]

@SkymanOne let me know if this PR is helpful or not, otherwise I can just close it.

I will come back to it after all my issues in cargo-contract are closed