Parity with System.Web.MimeMapping.GetMimeMapping for some MS extensions

[ipetrouchtchak-fi]

Would it possible to add mappings for some of the missing Microsoft extensions, which are found in System.Web.MimeMapping: https://github.com/microsoft/referencesource/blob/master/System.Web/MimeMapping.cs

AddMapping(".jfif", "image/pjpeg");
AddMapping(".mht", "message/rfc822");
AddMapping(".mhtml", "message/rfc822");
AddMapping(".one", "application/onenote");
AddMapping(".vdx", "application/vnd.ms-visio.viewer");
AddMapping(".vsx", "application/vnd.visio");
AddMapping(".vtx", "application/vnd.visio");
...

[viceice]

feel free to open a PR 🤗

[ipetrouchtchak-fi]

Opened a PR on mime-db: jshttp/mime-db#335 (comment)