Social Menu & Social Media Icons: Add dev.to support

#### Steps to reproduce the issue

1. Add link to https://dev.to in Social Icons widget or Social Menu.
2. View site.

#### What I expected

As the icon, I expect to see the DEV logo.

#### What happened instead

I see a generic "link" icon.

Here is an SVG of the dev.to logo:
https://gist.github.com/alexcarpenter/5e5772136ed711cd9fd8089c5ac76ea8

Jetpack already provides support for many social networks. Please consider adding support for dev.to, so I don't have to write custom support for it in a theme or plugin.

Start by tracing how the Social Icons widget and Social Menu map supported URLs to icons, then compare the existing mappings with the dev.to URL described in the reproduction steps. Done means a dev.to link displays the DEV logo instead of the generic link icon in both contexts.

Written by the indexing model from the issue text.