`ReadyState` is ambiguous

[japgolly]

We have ReadyState as closed | ended | open which is currently being used in MediaSource.

The problem is that there are many ReadyState definitions depending on where it's used. For example, IDBRequest.readyState is pending | done.

We should add types for all (or at least some common) ready state enums, and prefix them all according to their domain.

> rgs ' readyState: '
dom/src/main/scala/org/scalajs/dom/MediaSource.scala
16:  def readyState: ReadyState = js.native

dom/src/main/scala/org/scalajs/dom/RTCDataChannel.scala
33:  def readyState: RTCDataChannelState = js.native

dom/src/main/scala/org/scalajs/dom/IDBRequest.scala
52:  def readyState: String = js.native

dom/src/main/scala/org/scalajs/dom/MediaStreamTrack.scala
44:  val readyState: MediaStreamTrackState = js.native
110:      readyState: js.UndefOr[String] = js.undefined, remote: js.UndefOr[Boolean] = js.undefined,

dom/src/main/scala/org/scalajs/dom/HTMLDocument.scala
50:  def readyState: String = js.native

dom/src/main/scala/org/scalajs/dom/EventSource.scala
36:  def readyState: Int = js.native

dom/src/main/scala/org/scalajs/dom/FileReader.scala
26:  def readyState: Short = js.native

dom/src/main/scala/org/scalajs/dom/HTMLElement.scala
65:  var readyState: js.Any = js.native

dom/src/main/scala/org/scalajs/dom/TextTrack.scala
16:  var readyState: Int = js.native

dom/src/main/scala/org/scalajs/dom/WebSocket.scala
28:  def readyState: Int = js.native

dom/src/main/scala/org/scalajs/dom/XMLHttpRequest.scala
33:  def readyState: Int = js.native

[armanbilge]

Yes I realized this issue as well and brought it up in #588 (comment). What I ended up doing is checking what Typescript does, which is use this one for MediaSource. Of course, we don't have to follow typescript.

type ReadyState = "closed" | "ended" | "open";
type DocumentReadyState = "complete" | "interactive" | "loading";
type IDBRequestReadyState = "done" | "pending";

[japgolly]

Yeah let's not follow Typescript, clearer is clearly better IMO. I'll PR this now. I'm done with my RC1 testing 🚀

[japgolly]

btw, thanks for pasting those ts definitions! saving me work ❤️