Summary:I've tested this manually, but I'm not sure how to write a test for this. Hopefully someone can help out there. The least I could do is provide a starting point for a PR to be accepted.
Additionally, I've renamed the existing `NSLineBreakMode` enum converter (inside `RCTConvert`) to use dashes in the names instead of camelcase (eg: `word-wrapping` instead of `wordWrapping`).
Fixes#6338
Closes https://github.com/facebook/react-native/pull/6339
Differential Revision: D3052391
Pulled By: nicklockwood
fb-gh-sync-id: 1536dfc139d7995095e9ee9d5f13ca86f90783c5
shipit-source-id: 1536dfc139d7995095e9ee9d5f13ca86f90783c5