Edit Quick Reactions

### Your use case

#### What would you like to do?
I would like to be able to edit the list of "Quick Reactions" at the bottom of the emoji picker on desktop.
#### Why would you like to do it?
I find myself not commonly using those reaction emojis, and as a replacement I end up using the "Frequently Used" section instead. I already have some opinions about the rocket emoji being a default as well, so I would argue it's not a good idea to prescribe that list of emojis with no alternative.
#### How would you like to achieve it?
I, personally, would implement this by replacing the last emoji slot in the list with an edit button that would open a menu to select an emoji for each slot.

### Have you considered any alternatives?

I could also imagine it being implemented as a right click action, where right clicking a quick reaction would open the aforementioned menu, potentially with a short context menu entry, but this may not be very intuitive.
I have also considered it being in the settings menu itself, but I recall reading that you are trying to keep the number of user customizations small, and this seems a bit frivolous to be in that section.

### Additional context

_No response_

The issue does not name files, tests, or an entry point. Start by locating the desktop emoji picker and its Quick Reactions implementation, then review existing customization patterns; done means users can edit the listed reaction slots through an understandable interface.

Written by the indexing model from the issue text.