Add emoji-related tests for the font chain

1. Check that all emoji characters are supported in emoji fonts.

2. Check that no default-emoji characters are included in any font
that can get a higher score then the color emoji font, either by
being before it or by having a language/script assigned.

Bug: 26187231

Change-Id: Ic76bf59f1c6f9d2d290b1b64128d725ae08dcb5c