Antialiase plugin thumbnails

[iwoithe]

Resolves: N/A

This PR fixes a subtle, but visible, sharpness to the plugin thumbnails.

Before

After

• [x] I signed the CLA
• [x] The title of the PR describes the problem it addresses
• [x] Each commit's message describes its purpose and effects, and references the issue it resolves
• [x] If changes are extensive, there is a sequence of easily reviewable commits
• [x] The code in the PR follows the coding rules
• [x] There are no unnecessary changes
• [x] The code compiles and runs on my machine, preferably after each commit individually
• [x] I created a unit test or vtest to verify the changes I made (if applicable)