Add support for solidity structs

[zemse]

Example:

struct Amount {
    address token;
    uint96 value;
}

// before
function deposit(amount: {token: string, value: BigNumberish}): Promise<ContractTransaction>;


// after
export type AmountStruct = {token: string, value: BigNumberish};

function deposit(amount: AmountStruct): Promise<ContractTransaction>;

Closes #398

[changeset-bot]

🦋 Changeset detected

Latest commit: a55e6c4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@typechain/ethers-v5	Minor
typechain	Minor

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Click here if you're a maintainer who wants to add another changeset to this PR

[hasparus]

Nice one! I actually asked Krzysztof about emitting struct types earlier this week, and reading this gave a better insight into TypeChain internals :)

The only comment I have is a nitpick about naming of insertStruct — have you considered registerStruct? It wasn't obvious to me what insertStruct does before reading the implementation. Feel free to disregard this comment — it's just something that's been on my mind that I wanted to mention.

The PR looks good to me.

[zemse]

I just made the change for the name, registerStruct definitely makes better sense. Now just rebasing for this conflict problem.

[krzkaczor]

Nice work!

One last thing is a missing changeset. While writing one could you attach an example of how newly generated code is different from the old one?