Escaped underscores within Korean emoji shorthand have broken

[yhatt]

Slack is now available in Korean and Slack users can use Hangul as the name of custom emoji and emoji alias. Well, the Korean emoji shorthand brings #98 again:

<Blocks>
  <Section>
	<p><Escape>_:white_check_mark:_</Escape></p>
	<p><Escape>_:체크표시_초록:_</Escape></p>
  </Section>
</Blocks>

It appears that the escaped underscore inside emoji shorthand also has broken rendering.

We have to fix and recover emoji rendering by preventing escape for underscore within Korean emoji shorthand. Additional Unicode blocks Slack accepts as emoji shorthand are following:

• Hangul Jamo (U+1100 - U+11FF)
• Hangul Compatibility Jamo (U+3130 - U+318F)
• Hangul Jamo Extended-A (U+A960 - U+A97F)
• Hangul Syllables (U+AC00 - U+D7AF)
• Hangul Jamo Extended-B (U+D7B0 - U+D7FF)