Display tooltips for emoji reactions.

Problem to solve

I have members of my team who aren't terribly emoji-savvy, or have eyesight which isn't great. Recognising what an emoji is supposed to represent can be hard for them. Comments in Markdown have a tooltip, but the tooltip for reactions only displays the name of the person who left it.

Proposal

Display tooltips with the text: [User, user, and user] reacted with [:emoji_name:]