Consider adding a describe_error function to error types

[bcpeinhardt]

Howdy!

There's a particular pattern that's popped up in some Gleam packages, where modules that expose an error type Error also expose a fn describe_error(e: Error) -> String for stringifying said error. This functionality is especially helpful for logging in application code or using an ad hoc error type like the one provided in the snag package.

I wonder if we could implement this pattern in the stdlib. I have a PR showing what this might look like for the DecodeError type in the dynamic/decode package here. To be clear I have no strong opinions about the format of the error at the moment.

Off the top of my head, I don't know if any other module in the standard library exposes a custom error type.

I think a function like this might be useful for libraries using the decode module as well, for example: gleam/json exposes an error type that wraps the DecodeError

[lpil]

What would be the use cases for this function? For logging a generic English message might be enough, but should one be logging decode errors? I think probably not.

For other use cases is there a one-size-fits-all option? What about internationalisation?