Also, refactor ESLint and stylelint config files; now everything will work from our root dir.

* Deprecate hover media query shim and mixins

Fixes #25195.

This never was completed or fully implemented, and the docs are inaccurate as to what browsers are currently affected by this stickied hover problem. This PR aims to update the docs and deprecate the shim from our mixins and only return the pseudo-classes. To reflect the order of these states used elsewhere (e.g., our button styles), I've also updated the order of each within the mixin.

* Mention in docs and variables that it's deprecated

Due to a severe performance bug in Chrome (see https://bugs.chromium.org/p/chromium/issues/detail?id=800522) and due to the fact that (with the exception of IE/Edge on Windows desktop with touchscreen) all modern browsers now optimize the click delay away anyway, this optimization is not needed.

Closes https://github.com/twbs/bootstrap/issues/24670

The latest shipping version of Edge supports position: sticky and I've successfully tested it with Bootstrap 4 and it works as intended. I added IE10 in place of Edge in that note as I assume that IE10 also has the `position: relative` fallback.
REF: https://caniuse.com/#search=sticky

* Add min-width to body when printing

This should address some inconsistencies between browsers when printing. It applies a min-width to the body so that the content better resembles what your might see on your screen. I've made it a variable for easy customizing, too.

* Don't underline buttons when printing

* Add basic print styles for page and body size to create a semi-consistent print experience across browsers

Includes simplifying the prose in `tables.md` and adding the bug to the list of browser bugs.

Closes https://github.com/twbs/bootstrap/issues/25166

* Add some documentation on using CSS vars

Fixes #25147

* link to MDN doc

* Add additional form validation examples

Fixes #24811.

This adds .valid-feedback to our custom styles and server side examples; previously we ommitted this to suggest you don't always need valid feedback. In addition, this adds examples of the .{valid|invalid}-tooltip classes with a new subsection in the Validation docs.

* Update validation tooltip styles to remove fixed width; instead should retain itself to the parent element

* update ids

* finish docs paragraph, mention position: relative

Fixes #25168

- Drops the hover-focus mixin for standard :hover
- Adds explicit :focus styles to match button, input, etc with a box-shadow
- Adjusts z-index values to ensure the layers go initial, hover, active, focus

Fixes #24838.

* Remove incorrect roles from accordion, tweak/expand accessibility info
* Use `<button>` elements rather than links for the accordion

Merge branch 'docs-border-utilities' of https://github.com/ysds/bootstrap into ysds-docs-border-utilities

The append and prepend classes vertically aligned items in the center
For textareas this meant the addon would aling vertically instead of stretch and have it's contents vertically aligned
these changes fix that so everything is aligned how it should be

This commit allows nested structures for accordions. Also a part of
the documentation about data-children is removed because this
functionality didn't work and it's not applicable anymore.

Tests with the collapse accordion are also a bit adjusted to the new
situation.

* Base the outline button :active color on the background, fixing a contrast issue

* Only apply focus outline to active when it's focused