Fixes #21956

* Make container in navbar to occupy full width even on smallest breakpoint

* Fix typo in comment

* Apply fix only on smaller breakpoint

* drop the comment as chrome doesn't have a bug here

* Change it's to its.

* Fix links

* Fix typos

Remove .navbar-divider; it's undocumented and wasn't updated with the flexbox navbar updates, so it's kinda bunk right now

this was mad confusing for awhile

- since we're column to start, need to set row.
- note that flex-direction cannot be inherited, so we have to set it twice.
- apply the horizontal padding again to .nav-link.
- remove the .nav-item styles (un-needed).
- remove previous .nav-link styles as they were un-nested and potentially problematic in old placement should someone mix more navs in here.

since we're no longer using the .nav as a base class, we need to bring over some base styles for redoing browser list styles and setting flex in motion.

also brings with it some .nav-link styling. we're still using this global class, but with this small modification for alignment of content in responsive modes.

- Require inner element for the icon for improved customization (e.g., drop the element to replace it with your own icon font or SVG)
- Tighten up padding
- Better comments

fixes #18115: move forward with one naming scheme for inversed color schemes, renaming .navbar-dark to .navbar-inverse (matching .card-inverse in the process and restoring v3's inverted class name)

move all nav link and collapse and container behaviors to the toggleable class generation area; this way the .navbar-toggleable-* goes on .navbar, easily affecting everything that needs updating for each breakpoint's use

move padding on nav links and brand to be responsive padding, keeping mobile contents aligned better

- drop the table styles, use flex
- remove commented out code
- consolidate styles a bit
- add a huge flex-grow to the nav, making the assumption you want nav to take up most space

* Remove comment that duplicated some code
* Use transition mixin whenever possible
* Create a new function to reduce duplication
* Use the new `breakpoint-infix` method

* 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* Fix outdated classes to use newer ones