Prepare to implement tracked storage, RFC#669

[NullVoxPopuli]

Motivation here is that I want to stop folks from using https://github.com/ember-polyfills/ember-tracked-storage-polyfill (and swap its implementation to use the real implementation (here, hopefully)

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This doesn't make sense to continue work on until

• Bring @glimmer/component into ember repo #20751

lands -- because I don't really want to continue the fake-glimmer packages we have in @ember/-internals/metal

Additionally, this RFC, https://rfcs.emberjs.com/id/0669-tracked-storage-primitive#re-implementing-tracked-with-storage, kinda just likes like Starbeam concepts, so it should be super easy:

export function trackedStorage(...) {
  return Cell(...);
}

export function getValue(cell) {
  return cell.current;
}

export function setValue(cell, value) {
  return cell.set(value);
}

ez