Created by: andresgalante
During this clean up: https://github.com/twbs/bootstrap/commit/cd22eb1da03d5dbc9062ad5c9e75c05429e4bcd0 we removed the focus state indication for btn-link. Even though links don't have an underline and btn-link should mimic links they are missing some indication of the item been focus.
This PR closes #24720 (closed) and brings back the underline. Thanks @timfish