Keyboard shortcut to preview markdown doesn't work on OKR and Key Result descriptions

Summary

The cmd+shift+p shorcut to switch between markdown edit and preview doesn't work on OKR and Key Result descriptions.

Note: it does work when commenting on an OKR or Key Result.

Steps to reproduce

1. Open an OKR or Key Result work item
2. Edit the description
3. Make sure to use the Markdown edit mode (not Rich Text)
4. Press cmd+shift+p (MacOS) or ctrl+shift+p

Example Project

What is the current bug behavior?

1. The editor stays in markdown edit mode and doesn't switch to markdown preview

What is the expected correct behavior?

1. The editor switched to markdown preview

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes