During model transform preserve the argument passed to this.subject

[jbryson3]

During my conversion to 0.14 testing api, I found that all the arguments I was passing to this.subject() in my model tests were getting blown away.

//input
let model = this.subject({key: 'value'})
//output
let model = this.owner.lookup(%model%).createRecord();

This PR will preserve the argument passed to this.subject

//input
let model = this.subject({key: 'value'})
//output
let model = this.owner.lookup(%model%).createRecord({key: 'value'});

[Turbo87]

thanks 🙏