Allow arbitrary property access on event arguments

[HenryNguyen5]

The current typing for Event['args'] does not allow for us to use the added properties, since typescript will error out and say that the property does not exist on the type of Array.

For example, let's say that we have the event with the arguments foo and bar.

const tx = await myContractInstance.myMethod()

// gives us an event of { 0: '0xDEAD', 1: '0xBEEF', foo: '0xDEAD', bar: '0xBEEF' }
const receipt = await tx.wait()

// works
receipt.events.args[0] // 0xDEAD

// does not work, property does not exist on type Array<any>
receipt.events.args.foo // 0xDEAD

This PR fixes that, so that we can access arbitrary properties on our args arrayish-object.

[ricmoo]

I like this idea! I tried doing something like this before, but had no idea how to syntax it... I may pull this up and use it in a more generic sense. Let me look into it. :)

[HenryNguyen5]

Sweet, let me know if you have any syntax questions for making it more generic, happy to help

[ricmoo]

I've added this in 5.0.0-beta.164. Try it out and let me know if I pulled it in correctly. :)

I moved this up to the AbiCoder level and return it from the .decode method.

[HenryNguyen5]

Would you be able to backport this to 4.x? We haven't used 5.x yet since its not marked as stable

[ricmoo]

I'm a little apprehensive about changing this in v4 with TS 2.9. The last seemingly innocent change to the types broke a bunch of people, which I'd like to avoid. I agree this should be backwards compatible, but v5 is so close, I'd rather hold off... Make sense?

[HenryNguyen5]

Sounds good to me @ricmoo

[ricmoo]

Awesome! I'll close this PR then (it has been merged into v5).

Thanks! :)