Embroider: Use of ember-data internals

[fsmanuel]

Similar to #739 we use ember-data internals to detect if ember-data is installed and if it's a DS.Model, DS.ManyArray, or DS.PromiseManyArray .

function requireModule(module, exportName = 'default') {
  if (require.has(module)) {
    return require(module)[exportName];
  }
}

const DS = requireModule('ember-data');

export function isDsModel(o) {
  return !!(DS && o && o instanceof DS.Model);
}

export function isDSManyArray(o) {
  return !!(
    DS &&
    o &&
    isArray(o) &&
    (o instanceof DS.PromiseManyArray || o instanceof DS.ManyArray)
  );
}

I wonder how long the ember-data import will be arround and if @ember-data/model/-private could be an embroider safe alternative.

const Model = requireModule('@ember-data/model');
const { ManyArray, PromiseManyArray } = requireModule('@ember-data/model/-private');

//cc @runspired @ef4 @gilest

[runspired]

isDSManyArray should just go away.