EventedConstructor incorrectly typed

`Evented` isn't created with `declare`. It's a traditional es5 class function.

```
define(["./aspect", "./on"], function(aspect, on){
// module:
// dojo/Evented

"use strict";
var after = aspect.after;
function Evented(){
// summary:
// A class that can be used as a mixin or base class,
// to add on() and emit() methods to a class
// for listening for events and emitting events:
// example:
// | define(["dojo/Evented", "dojo/_base/declare", "dojo/Stateful"
// | ], function(Evented, declare, Stateful){
// | var EventedStateful = declare([Evented, Stateful], {...});
// | var instance = new EventedStateful();
// | instance.on("open", function(event){
// | ... do something with event
// | });
// |
// | instance.emit("open", {name:"some event", ...});
}
Evented.prototype = {
on: function(type, listener){
return on.parse(this, type, listener, function(target, type){
return after(target, 'on' + type, listener, true);
});
},
emit: function(type, event){
var args = [this];
args.push.apply(args, arguments);
return on.emit.apply(on, args);
}
};
return Evented;
});
```

This needs fixing:

```
interface EventedConstructor extends _base.DeclareConstructor {
new (params?: Object): Evented;
}
```

Locate the EventedConstructor declaration in the Dojo typings and compare it with the Evented ES5 constructor shown in the issue. Update the declaration to reflect that constructor, then run the repository's available TypeScript validation or typing checks to confirm it is accepted.

Written by the indexing model from the issue text.