Summary:
fix the regression I mentioned in https://github.com/facebook/react-native/pull/15162#issuecomment-319696706
as no one is working on this, I take the step, although I know nothing about Objective C
I find the key point is that the keys in `NSDictionary` are not ordered as presented, it's a hash table, so no grantee on keys order, so I create a new array to do that, then it will check `ultralight` before `light` and `semibold` before `bold`
Closes https://github.com/facebook/react-native/pull/15825
Differential Revision: D5782142
Pulled By: shergin
fbshipit-source-id: 5346b0cb263e535c0b445e7a2912c452573248a5
d3007b0fd2