Add Filter Support with Infura provider implementation for fetching events

[kshinn]

This PR addresses #1814 & #1798

With regards to getLogs calls in general, Infura prefers clients use getFilterChanges it ends up being more efficient than the vanilla getLogs and since it is cursor based it ends up being a more consistent set of data.

The changes enable these methods to become generally available to the providers to use as:

let filterId = await provider.newFilter({ topics: [...] });
let updatedLogs = await provider.getFilterChanges(filterId);

Additionally, I've extended the Infura provider to utilize these methods in the event emitter system in order to better service the Contract convenience methods.

[kenerwin88]

Need this desperately. Any chance it can get merged?

[zemse]

These methods are used internally in provider.on. While this PR is being looked at, you may use the send API for now.

let filterId = await provider.send('eth_newFilter', [{ topics: [...] }]);
let updatedLogs = await provider.send('eth_getFilterChanges', [filterId]);

[ricmoo]

I didn't add filter support in v5 (it is the default in v6), but I've made changes that should accomplish the same goal in v5.6.

The main reason to hold off on switching to filter ID is that it affects how the FallbackProvider works. In v6, the entire event model has been redesigned so things like filter ID are more friendly.

Please try it out and let me know if you still have any problems. :)

[kenerwin88]

Wow, thank you so much @ricmoo! Really appreciate it, and will try it out ASAP!

[ricmoo]

Closing this now; the issue has been fixed by keeping a larger window to capture getLogs results with no entries which solves the underlying problem for v5 and in v6, uses a solution similar to the one proposed in this PR. :)

Thanks! :)