Add Stack component (#2152)

* Add Stack component

* Stylelint auto-fixes

* Ongoing Stack component implementation

* Add Stack dividers, responsive props, examples

* Implement align, alignWrap, and spread props

* Code cleanup

* Wrap responsive props under narrow+regular queries

* Fix structure comment

* Address rendering bugs, add docs

* typo

* Cleanup

* typo

* Please stylelint

* Update docs/src/stories/components/Layout/Stack.stories.jsx

Co-authored-by: Mike Perrotti <mperrotti@github.com>

* Simplify jsx

* Simplify Stack CSS, add Stack-item

* Add Stack feature stories

* Stylelint auto-fixes

* Remove `none` from dividerAriaRole property

* add wide viewport support

* Stylelint auto-fixes

* Add changeset

* Hide custom gap support

* Use Sass comments instead

Co-authored-by: Actions Auto Build <actions@github.com>
Co-authored-by: Mike Perrotti <mperrotti@github.com>

.changeset/thick-coats-yawn.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": minor
+---
+
+Add Stack component