Re-enable disabled emoji tests

Since Ib68f803c6adfb41db70f7319b7736d17cdbb6ec2 updates the emoji
data to version 4.0 beta, we can now re-enable the disabled emoji
tests.

Also fix some style issues, update data file parsing method to handle
the new emoji format, add UN to unsupported flags, and do a little
refactoring.

Bug: 26187231
Change-Id: I441fdfed68381d08e5e0b3af91e94bfae742eef6