* add 'lighter' and 'bolder' font weight classes
these are 2 special values for font weight, that will give their content a font-weight value of 100 more or less than their inherited font-weight.
probably doesn't fully fulfill this issue, https://github.com/twbs/bootstrap/issues/23969, but it's a start
* Update .stylelintrc
* add 'lighter' and 'bolder' variables per @mdo 's request.
* Making use of `prefers-reduced-motion` media query
As discussed in #25249 - if a user (Who is using Safari / iOS) requests
reduced motion in their system settings, we should avoid transitions.
* Ignoring prefers reduced motion for CSS Linting
* Updating copy clarifying the reduce motion functionality in accessibility.md
