fixes #17573

Despite now having the ability to override outline-variant color, it's not actually being used so each are still #fff

Related: https://github.com/twbs/bootstrap/pull/20734

— Moves print display utils to display utils file
— Removes all other .hidden- utils
— Expands on .invisible and it's mixin to provide options for visibility: visible and visibility: hidden

— Rename display docs page
— Move print display utils to display utils page
— Drop remaining of responsive utils page as it's being replaced with display utils
— Update nav to reflect changes

* Drop -x and -y as they're all the same
- Also move -width to elsewhere in the vars because it makes no sense by spacers.
- Update values of -x and -y across main Sass and docs Sass.
* Update docs to reflect changes; link to spacing utils from options page

Update Google sourcemap resources link

Based on this pen: http://codepen.io/zalog/pen/jyoyoR

In addition to #22011 and #21994

* Remove 'hover' from variable names
* Fix indentation in variables

Re-arranged contextual rows/cells so that example HTML matches example result.

normalize is no longer part of BS

Change 'has no affect' to 'has no effect' in Modal documentation