Created by: pricop
This is a backport from BS5 to BS4.
It fixes https://github.com/twbs/bootstrap/issues/35553 (for the vast majority of cases) and also increases text legibility.
The small-font-size will actually increase from 13px to 14px with this change. Personally I prefer doing it the BS5 way (14px), as the text is more readable now.
If it's needed, I can do another PR with the $small-font-size: .8125rem !default; to resemble BS4 more closely but I feel like this would be a move forward even for BS4.