[Feature Request]: Thumbnail preview for `pdn` files

[TrigamDev]

Checklist

• [x] I am using an up-to-date version.
• [x] I have read the documentation.
• [x] I have searched existing issues.

Description

There are currently no thumbnail previews for pdn files (the project file format for Paint.NET).

Solution

Add a thumbnail renderer for pdn files.

Alternatives

No, pdn files currently have the default, blank thumbnail.