Deprecate window.ENV

[chancancode]

We should only use window.EmberENV (usage of window.ENV is discouraged, and only exists as a form of legacy support). I’ll do a separate PR to add a deprecation if we find and use window.ENV.

- @rwjblue in #18372

[rwjblue]

The basic idea here is to refactor this:

ember.js/packages/@ember/-internals/environment/lib/env.ts

Line 244 in 7e89ec1

})(global.EmberENV || global.ENV);

To check if we are falling back to global.ENV and issue a deprecation if we do. Something like:

let providedEnv = global.EmberENV;
if (providedEnv === undefined) {
  providedEnv = global.ENV;

  deprecate(
    'Configuring Ember\'s boot options via `window.ENV` is deprecated, please migrate to `window.EmberENV` instead.',
    providedEnv === undefined,
    {
      id: 'ember-environment.window.env',
      until: '3.17.0',
    }
  );
}

(EmberENV => {
  // ...snip IIFE contents...
})(providedEnv);

[rwjblue]

Closed by #18441