Add Cmd.debounce

[TimLariviere]

Following #1061, add a Cmd.debounce helper to debounce events like Entry.TextChanged, etc.

Usage:

type Model =
    { EntryValue: string
      ValidatedText: string }

type Msg =
    | TextChanged of string
    | TextValidated of string

let validateTextCmd =
    Cmd.debounce 300 (fun value ->
       TextValidated value
    )

let update msg model =
    match msg with
    | TextChanged newValue -> { model with EntryValue = newValue }, validateTextCmd newValue
    | TextValidated value -> { model with ValidatedText = value }, Cmd.none

let view model =
    VStack() {
        Entry(model.EntryValue, TextChanged)
        Label($"Validated text: {model.ValidatedText}")
    }