Refactor carousel

drop the fixed width of the indicators. instead use the carousel-control width as margins to ensure content doesn't overlap

Move margin from adjacent selector to right on the .custom-control for better responsive rendering (#21295)

- fix naming of left/right controls
- drop the absolute positioning of things and rely on only 3d transforms
- remove img styles and require classes to avoid inline-block line-height stuff

grid-breakpoint for sm is 576px
https://github.com/twbs/bootstrap/blob/v4-dev/scss/_variables.scss#L186-L192

1._breakpoints.scss
comment  says that grid-breakpoint for sm is 544px,

2.http://v4-alpha.getbootstrap.com/layout/overview/#responsive-breakpoints
current document says that grid-breakpoint for sm is 544px,
but it should be 576px

* Make /utilities/ redirect to /utilities/borders/.

* Rewrite sidebar active link logic to ensure superstrings are not selected.

https://webkit.org/b/150079 has been fixed!
Refs #14975

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