accounts/bind/v2: generate TryPack* methods

[mask-pp]

1. Fix the error return format.
   todo: bindtype needs more complex logic to fix it.
   if err != nil { return nil, err } if err == nil { return obj, nil }
2. Return pointer type object to avoid copying the whole struct content.
3. Give the panic decision to the user.
4. Fix empty line at the end of function.

TODO: fix some related test cases.

[mask-pp]

@MariusVanDerWijden If these changes make sense, then I will fix the related test cases.

[MariusVanDerWijden]

LGTM, I agree with @mask-pp that we shouldn't have panic'd on Pack, but this is a good workaround imo