Mention rendering issues when using allowedMentions

[eritbh]

@mushroom-disaster you probably have more information about what platforms/scenarios actually cause issues than I do, but my understanding is:

• Using allowedMentions to disable a mention from pinging someone also prevents that user's user information from being applied to the mention in some clients, resulting in broken-looking mentions
• We currently use allowedMentions in .whois output to prevent every mod who's added a note to the user from getting pinged
• Embeds never send pings for mentions inside them and should probably render more consistently, but the output UX would have to be reworked to accommodate the embed fields

So we need to figure out how exactly we want to move forward with that