Deprecating Ember Array

Summary

Deprecate Ember.Array, Ember.MutableArray, Ember.ArrayProxy, Ember.NativeArray, Ember.A, Ember.Enumerable and Array computed macros.

Motivation

Now that Ember has a proper tracking system and the availability of tracked-built-ins we no longer need our own custom arrays. In addition, much of the internal implementation relies upon Mixins which we also hope to deprecate in the future.

Transition Path

All uses of custom Arrays should be replaced with native Arrays and tracked-built-ins. Additionally, computed macros should be updated to use tracked getters.

Given how estabished these patterns are, we probably want to provide an addon that brings back at least some of the functionality to aid migration.

Exploration

To validate this deprecation, I've tried removing EmberArray in this PR: https://github.com/emberjs/ember.js/pull/20921

How We Teach This

We should replace any references in the guides with native arrays or TrackedArray.

Drawbacks

This functionality is old and very well established, removing it will not be without pain to many users.

Alternatives

Deprecate just Ember.A: #864

Unresolved questions

None

Notes

This overlaps with #1112 which also seeks to deprecate Ember.ArrayProxy.