Generate series of `.table-responsive-*` classes to accomodate overflowing tables in a variety of screen sizes

Rename `.table-inverse`, `.thead-inverse`, `.thead-default` to `.table-dark`, `.thead-dark`, `.thead-light` respectively

(#22414) Rename variables `$table-inverse-bg`, `$table-inverse-accent-bg`, `$table-inverse-hover-bg`, `$table-inverse-border-color`, `$table-inverse-color` to `$table-dark-bg`, `$table-dark-accent-bg`, `$table-dark-hover-bg`, `$table-dark-border-color`, `$table-dark-color` for consistency

Rename for consistency `$table-sm-cell-padding`, `$table-bg-accent`, `$table-bg-hover`, `$table-bg-active`, `$table-inverse-bg-accent`, `$table-inverse-bg-hover` to `$table-cell-padding-sm`, `$table-accent-bg`, `$table-hover-bg`, `$table-active-bg`, `$table-inverse-accent-bg`, `$table-inverse-hover-bg`, respectively (#22414)

* Rename variable $input-border-focus to $input-border-color-focus
* Rename variables $pagination-hover-border, $pagination-active-border, $pagination-disabled-border to $pagination-hover-border-color, $pagination-active-border-color, $pagination-disabled-border-color, respectively
* Rename variables $state-*-border to $state-*-border-color, respectively
* Rename variables $alert-*-border to $alert-*-border-color
* Rename $list-group-active-border to $list-group-active-border-color
* Rename $table-inverse-border to $table-inverse-border-color
* Rename $btn-*-border to $btn-*-border-color
* Rename $navbar-*-toggler-border to $navbar-*-toggler-border-color

* Get this party started by removing mention of Normalize.css

* Nuke the old comment, consolidate to a single line and number as appropriate

* Bring over styles for HTML element from Normalize to Reboot

* Move margin override for body element from Normalize to Reboot

* Drop the block reset for HTML5 elements in IE9- from Normalize given we dropped IE9 support

* Building on previous commit, do the same thing for figure, figcaption, and main

* Remove IE9- display from Normalize given our browser support

* Drop IE8 figure margin because we're IE10+

* No need for the h1 overrides because we reset these font and margin styles anyway in _type.scss already

* Drop Safari 6 b and strong normalization because we're Safari 8+

* Remove mark styles for IE9- from Normalize

* Remove old iOS audio fixes from Normalize

* Remove IE9- display for progress from Normalize

* Remove more IE9- rules from Normalize

* One more IE9- display removal for canvas element

* Move pre overrides from Normalize to Reboot

* Move over some link resets to Reboot, drop others

- Move over background-color and text-decoration
- Drop focus outline change given it affects the offset on hover of
focused links

* Move over more code element resets, consolidate with pre overrides, too

* Move over sub and sup wholesale

* Move over img normalization to Reboot

* Move over SVG override too

* - Drop dupe hidden, but add comment for it
- Move over template
- Move over summary

* Remove bulk of @viewport comment

* edit down that code comment

* consolidate html-based normalizations

* update comments

* Consolidate abbr styles

* move over more type elements

* move over hr changes

* move over form controls and more

* move over button resets

* move over firefox button changes

* move over search changes and more

* we nuke all these styles for fieldsets anyway, so outright remove them

* no need for those, we override them

* move over legend, fieldset, progress

* line break

* delete normalize file

* linting

* update comment

* clarify docs mentions of normalize and reboot

* remove normalize excludes from linter

* remove normalize excludes from cli task

* linting

* callout license since we forked part of normalize

* Improve comments, move table background reset to .table class instead of in reboot

* trailing space

Tried redoing this in flexbox, but it falls apart really quickly. Any changes in height of the cells throws it all off since the rows become columns (and thus, content across columns cannot be equally sized). Rather than implement something with such glaring flaws, I'm nuking it outright.

- Add inverse examples for all variants
- Use rgba() colors for hover and accent states for easy usage in inverse styles

- Rename -height to -height-base to match other vars
- Drop use of -height across the board and rely on it to be inherited
- Adjust padding of .dropdown-header to account for different line-height of h6 heading element (this needs refactoring for variables and rems also)

See the IE9 note in https://developer.mozilla.org/en-US/docs/Web/CSS/%3Ahover#Browser_compatibility
The prereqs to trigger the bug are still present in v4.
/fyi @mdo

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