Social Icons: Add a 'Phone' icon which takes a tel: link

[jordesign]

In addition to having the 'email' icon it would be great to have a 'Phone' icon as well - which could take a tel: link to automatically add a link to make phonecalls.

[jordesign]

Suggested in the Forums: https://wordpress.org/support/topic/phone-in-social-links-block/?view=all

[t-hamano]

I also think the "Phone" icon is necessary. However, we need to create an icon, so I would like to add a Needs Design label.

By the way, there is a Phone icon in the dash icon. This dash icon is also used in the experimental form block's tel field.

[skorasaurus]

similar issue at https://github.com/WordPress/gutenberg/issues/32890; but since this one has a clearer title; I'll keep this one open.

[colinduwe]

Submitted a PR that adds the variation using the Dashicon. There are a couple things to consider:

1. The url isn't empty, it starts with 'tel:' as the url with isn't how any others work.
2. The description, "Display an icon linking to a social media profile or site.", isn't entirely appropriate here. I'm not sure if we can change that for variations.