Embedded image fix

[Tranquilite0]

The regex for matching data URIs was only matching MIME types consisting of word characters which means data URIs with valid MIME types like 'svg+xml' would be rejected. Looking at the list of registered mime types (https://www.iana.org/assignments/media-types/media-types.xhtml) I determined that the regex should also match ., -, and +.

Also I had some data URIs with embedded .emf files so I updated knownContentType to allow .emf files.

[onizet]

That's an amazing PR! Thanks for that submit.
One point: you should not remove the .ConfigureAwait(false) because this is needed for .Net 4.8 (and ASP.Net WebForms) which lacks a proper support of async.
Can you please restore that removed line from your PR?

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Tranquilite0]

Good catch, I didn't intend to make that change. Also I tried to make the requested change through GitHub directly, and now it is showing all lines as changed? Did GitHub just redo all the line endings or something? This is my first time submitting a pull request through GitHub.

[onizet]

Yes, I think it messed up with the line ending. I define a editor.config file at the root of the project to unify the code along multiple developer. I'm not so familiar neither. I'm going to merge that PR and handle whitespaces if needed. Thanks for your support!