Allow `_` as a record field name

[DZakh]

_ isn't a valid name.

For:

type errorMessage = {
  _: string
}

I want to write a type for https://ajv.js.org/packages/ajv-errors.html#default-message

[cknitt]

Why not just do

type errorMessage = {
  @as("_") default: string
}

or something like that?

[DZakh]

It's possible to have a workaround. I just don't see a reason not to have _ as a field. It adds extra cognitive complexity when type value is different from the runtime one.