Add functions to validate URLs.

[enigmalea]

We should add functions to validate various types of AO3 URLs - i.e. is the provided URL a valid AO3 work URL? - and return a boolean response.

[gingerchew]

Were you thinking something like this:

const isAo3Url = ({ url: string }) => url.matches(/^https?:\/\/(archiveofourown|ao3).org/);

Or something that also fetched the work and validated the result?

[essential-randomness]

IIRC it was something like that. Not just isAo3Url, but also isWorkUrl or isAuthorProfileUrl or similar.