Render emojis

- Current behaviour: Emojis pasted in the input box are rendered properly in the output (which is desired), but emojis of the format `:point_up:` are rendered as plaintext rather than emojis.
- Required behaviour: Emojis of the format `:point_up:` should be rendered as emojis and not as plaintext in the output.

Start at the live preview’s input-to-output rendering path and inspect how Markdown text is parsed. Compare the existing handling for pasted emoji characters with the `:point_up:` case. Done means that colon syntax renders as an emoji in the output without regressing pasted emoji rendering.

Written by the indexing model from the issue text.