* Clean up some utilities

- Align CSS properties
- In `_spacing.scss`, we had a comment saying what 'a' was for, but we removed that so this comment no longer applies

* Remove '-xs' from `.navbar-toggleable-xs` and remove duplication

* Fix outdated classes to use newer ones

* Update clearfix to use block instead of table display (also reorder properties for linting)
* update docs snippet for clearfix mixin—was apparently still using Less syntax and had old clearfix hack (even before the block change in this PR)

When the rubberband effect causes Safari to scroll past the top of the
page, the value of scrollTop becomes negative. If the offset of the first
ScrollSpy target is 0 - essentially if the target is at the top of the
page - then ScrollSpy should not clear the active item. Conceptually, the
first item should remain active when rubberbanding past the top of the
page.

This commit fixes issue #21055 by verifying the first scrollspy target is
not at the top of the page before clearing the active nav-item.

* Clean up _flex.scss a little

This commit just cleans up the formating of _flex.scss by changing
it so that it uses a single `@include media-breakpoint-up` instead
of multiple. It also aligns all of the CSS properties so it looks
a bit nicer.

* Remove `-xs` from flex classes

Remove most border-radius properties and instead use overflow: hidden; to properly round corners of a full progress bar. (#21216)

Fixes #19065.

* fix form-inline with flex enabled
* grunt
* fix alignment of labels
* shorter if syntax
* add new form example to docs for now
* update inline form docs usage guidelines
* responsive margins
* better margin utils
* fix sizing of .form-check
* flexbox alignment of .form-check
* no need to change direction
* support custom controls in inline form, for default and flex modes
* add example of custom select and checks to docs
* remove hidden and visible label variants since we cover that in the usage guidelines at the start and include hidden labels everywhere
* use property value instead of layout name
* apply to all labels
* add a visible label, space it out
* add id

* Add rounded-0 class

* grunt

* add border utilities for removing borders

* clean up comments

* add basic border docs

* docs styles for border utils

Fixes #19107.

in carousel example, replace img-circle by rounded-circle css class

grid-breakpoint fix [document]

v4 disabled navbar links

Update .table-responsive

Wrap .fade and .collapsing transition properties in $enable-transitions

Tweak modal sizes

Button toggling - trigger change event on input. Fixes #16673, fixes #17599.

Carousel - Do not prevent on keydown for input and textarea