Adjusts tag link to avoid underlining spaces

What does this MR do?

Make a simple adjustment in tag link html structure to avoid drawing the underline text-decoration on white spaces, as pointed by @domnulnopcea at #38122 (closed).

Are there points in the code the reviewer needs to double check?

I'm really that comfortable with the adjustment I made in link_to to avoid a line break. Anyway, that was the only way I could make it work.

Why was this MR needed?

Whenever somebody put a <i class="fa ..."></i> inside an anchor (<a>) we are going to get issues with underlining, since the engine underlines the whole element, but the <i> avoid this with the text-decoration: none. So, I copied the .fa definition to a .fab ("b" comes from before) so we can use .fab whenever we want to add a FontAwesome icon before any element. I wanted to say this was my idea, but it wasn't.

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #38122 (closed)