Swipe view in merge request image diff: User select is not getting disabled

Summary

The user-select CSS is not getting disabled for swipe view on merge request changes, so the browser tries to select the image as you're dragging.

Steps to reproduce

• View merge request with a changed image
• Select swipe view
• Drag left and right

What is the current bug behavior?

Browser highlights image(s) as you're dragging

What is the expected correct behavior?

No selection highlight

Relevant logs and/or screenshots

gitlab-11.9-merge-request-swipe

Output of checks

This bug happens on GitLab.com

Possible fixes

I have a fix I will push for swipe viewer vue in a new MR shortly. Don't know if it's clean, but it's done the same way in onion skin viewer vue.

Suggested /label ~bug image diff