MDL-82210 output: Add support to FontAwesome families

The solid family was chosen by default when Font Awesome was upgraded
from 4 to 6, but FA6 has more families, like regular or brands.
This commit adds only the fa class to the icon when no other family
class is used.

admin/tool/componentlibrary/hugo/site/layouts/shortcodes/moodleicons.html

@@ -8,7 +8,7 @@
     <div class="small text-truncate" data-toggle="tooltip" data-placement="bottom" title="{{ .name }}">{{ .name }}</div>
     <div class="row g-0">
       <div class="col-sm-6 d-flex align-items-center justify-content-center">
-        <i class="fa {{ .icon }} fa-2x"></i>
+        <i class="{{ .icon }} fa-2x"></i>
       </div>
       <div class="col-sm-6 d-flex align-items-center justify-content-center">
         {{ .standardicon | safeHTML }}