Invalid filename suggestions

Problem/Motivation

When Twig Debug is enabled, the following error is in the DOM.

<!-- INVALID FILE NAME SUGGESTIONS:
   See https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Render!theme.api.php/function/hook_theme_suggestions_alter
   fontawesomeicon__fa-handshake
-->

Steps to reproduce

Proposed resolution

Replace hyphens with underscores in $variables['name'] in fontawesome_theme_suggestions_fontawesomeicon

Remaining tasks

Merge request to follow.

User interface changes

None

API changes

None

Data model changes

None