Allow pinging mentions in embeds

[WilcoM]

Currently there's no way to make working pinging mentions in embeds. They get formatted properly, but member data isn't gathered so people won't get pinged.

Bots use embeds more and more, and embeds make for a great design-choice of sending out bot responses and event notifications.

Even a new way of embedding pingable mentions could easily work, so the current usage of embedded mentions don't break.

For example
<@373912954057392138> ping disabled
<@%373912954057392138> ping enabled

[WilcoM]

I just had to revert the very neat and clean looking embeds above, to this;

I'm sorry you all have to see this, it could've been avoided if pinging mentions were allowed though.

[ckohen]

I wouldn't mind this necessarily, however the old functionality definitely needs to be kept intact. (We do have allowed_mentions which could very well be used for this btw)

I would like to mention that mentions - ha - in embeds were never truly supported, whether the mention resolves is luck of the draw, and mobile users rarely, if ever, see all mentions in an embed as resolved due to their more limited cache sizes.

So, I propose this:

• Short term: add mentions to embeds
• Long term: figure out something better that natively supports things like mentions. I decided to write up another feature request (Replace / Augment bot embeds with Adaptive Cards #4125) to explain a potential alternative since it got a little long and would fit better standalone

[WilcoM]

Yep, completely agree with keeping the current usage and functionality working as is. The proposed way of adding % to the mention code would allow to specifically ping certain roles/members, while only parsing but not pinging others.