Clarify why the AJAX helpers are deprecated

Author: japgolly

src/main/scala/org/scalajs/dom/ext/Ajax.scala

@@ -10,7 +10,7 @@ import scala.scalajs.js.typedarray.ArrayBufferView
 import scala.scalajs.js.typedarray.TypedArrayBufferOps._
 
 /** Wraps an XMLHttpRequest to provide an easy one-line way of making an Ajax call, returning a Future. */
-@deprecated("use the dom.fetch API instead", "2.0.0")
+@deprecated("scalajs-dom no longer includes custom utilities, only facades. Try using dom.fetch API which doesn't require additional utilities.", "2.0.0")
 object Ajax {
 
   /** Supported data formats for Ajax are implicitly converted to InputData */

src/main/scala/org/scalajs/dom/ext/AjaxException.scala

@@ -5,11 +5,11 @@ import org.scalajs.dom
 /** Thrown when `Ajax.get` or `Ajax.post` receives a non-20X response code. Contains the XMLHttpRequest that resulted in
   * that response
   */
-@deprecated("use the dom.fetch API instead", "2.0.0")
+@deprecated("scalajs-dom no longer includes custom utilities, only facades. Try using dom.fetch API which doesn't require additional utilities.", "2.0.0")
 case class AjaxException(xhr: dom.XMLHttpRequest) extends Exception {
   def isTimeout: Boolean = xhr.status == 0 && xhr.readyState == 4
 }
 
 // This is just there to work around some weird warnings in Scala 3.x
-@deprecated("use the dom.fetch API instead", "2.0.0")
+@deprecated("scalajs-dom no longer includes custom utilities, only facades. Try using dom.fetch API which doesn't require additional utilities.", "2.0.0")
 object AjaxException extends (dom.XMLHttpRequest => AjaxException)