Consider using nullness instead of Option to map null | undefined types

[MangelMaxime]

TypeScript documentation:

interface ConfigTypeMap {
        default: string | null;
    }

translates into

[<AllowNullLiteral>]
[<Interface>]
type ConfigTypeMap =
    abstract member ``default``: string | null with get, set

How should we represents optional properties and optional parameters?

interface ErrorHandling {
    error?: string | undefined | null;
}

interface PromiseLike<T> {
    a(onfulfilled?: string | undefined | null);
    b(onfulfilled?: string | undefined);
    c(onfulfilled?: string | null);
}

if we adapt todays logic it should become something like

[<AllowNullLiteral>]
[<Interface>]
type ErrorHandling =
    abstract member error: string | null with get, set

[<AllowNullLiteral>]
[<Interface>]
type PromiseLike<'T> =
    abstract member a: ?onfulfilled: string -> unit
    abstract member b: ?onfulfilled: string -> unit
    abstract member c: ?onfulfilled: string -> unit

will this still convey the correct meaning ?

We need F# 9 to land in Fable in order to support this feature.