docs(AuthWit): Add more examples and extend docs

[critesjosh]

The current references to the authwit patterns rely heavily on token examples. Create additional references and link to them in the docs.

Some additional use cases to consider:

• multisig accounts
• token transfers from other contracts. example here

[critesjosh]

Multisig contract notes here: https://docs.google.com/document/d/154RW7PZ2KPlo7RWh-hojh9qZ9ubNs8XCq33rSzSX9HI/edit#heading=h.887n9glyov61

branch: https://github.com/AztecProtocol/aztec-packages/tree/spetal/multisig

[critesjosh]

Document we return IS_VALID_SELECTOR instead of a boolean from is_valid? It’s due to risk of accidentally calling another function with the same selector or a fallback function that returns something that gets understood by the caller as a boolean. But it’s not documented anywhere.

https://docs.google.com/document/d/1BERcO9Aj1N9lU79pYWlJJiGfVDwMD680oVWJp_QI2QM/edit

[benesjan]

I was considering picking up this issue but the ikigai example is too outdated and unfinished to use it as reference and regarding the multisig it would make sense to wait for it to be merged so that we can use the #include_code macro without which it would most likely get outdated and broken.

@critesjosh Do you know what is blocking the multisig from being merged?

[critesjosh]

@spalladino did some low level hacking around the kernel circuits, iirc, and I'm not sure that the changes we made ever made it into master.

[spalladino]

They didn't, as they require calling a private function as unconstrained from a contract, which I don't know whether it's tracked.

[critesjosh]

closed by #6220