since the recordArrayManager already maintains the uniq index, we can use that to simply push the record onto the record array without needing the safety of addRecords dupe guard. This prevents another O(n) operation
prefer Object.create(null) for typeMap backing stores. Cache misses are faster, and won’t collide with prototype pollution
Merge pull request #2123 from emberjs/push-record

since the recordArrayManager already maintains the unique index, we can us...