Added fragment for Deferred Topic Filter

[lukastanisic99]

Subscribing with contract.filter.EventName(someValue...) returns the entire log object instead of returning the Event arguments to the listener. Other checks bellow check if fragment is present in the event but since it's an 'else if' it never triggers.

[lukastanisic99]

When you take a look at what's invoked when using the Deferred Topic Filter

ethers.js/src.ts/contract/contract.ts

Line 397 in ad5f1c5

return new PreparedTopicFilter(contract, getFragment(...args), args);

It also expects an Event Fragment and the typechain types that are generated also expect Event arguments instead of the full log object.
Taking all that into account it seems there is no 'design decision' not to include the fragment as part of the Deferred Topic Filter, so the PR is a fix to an intended and expected behavior.