Mentions pop-up doesn't close with Escape

## Bug Report

**Current Behavior**
The mentions pop-up doesn't stay closed when Escape is pressed.

**Steps to Reproduce**
1. Start mentioning a user
2. Press escape
3. Pop-up closed for a split second, then immediately reappears

**Expected Behavior**
Pop-up should stay closed.

**Screenshots**

https://user-images.githubusercontent.com/7406822/136935573-815b70e5-afd1-4ed8-aec5-059e0eb026aa.mp4

**Environment**
Discuss 1.1 pre-release & Demo 1.0 deployment

**Possible Solution**

I'm guessing that the pop-up is opened on `keypress`, and we don't filter out the escape key when deciding to open it.