Merge branch 'form-check-input-validation' of https://github.com/supergibbs/bootstrap into supergibbs-form-check-input-validation

Closes https://github.com/twbs/bootstrap/issues/25316

* Update copyright range to include 2018

* Extend copyright date range on new files from 2017 to include 2018

* Make dropright snippet the same as demo

* Add missing .dropdown-toggle-split class

* Make clear the split button label the same as demo

* heading for better linking

* tell folks where to start

* more headings

* required keys section added, closes #25293

* fix cover nav

* Improve signin visuals and alignment with that flexbox love

* rewrite cover example in flexbox

* lighten signin bg

* first pass at pricing example

* redo examples index with data file

* tighten up spacing a bit

* update navbar descriptions

* link pricing

* move that back

* property order

* Fix test errors.

* Compress pricing.png.

* add form validation example

* remove that

* rename that

* restyle and space out

* fix errors

* change order

* cleanup album css and styles

* tweak examples index

* make it a badge

* options

* improve sticky footer alignment

* redesign example index

* brand new blog layout

* start new screenshots

* new product example page a la apple

* add email field

* fix linter, remove unused blog css

* hook up feather icons to start

* redo dashboard

* fix linting

* add floating labels example

* formatting

* formatting

* lint

* fix values o...

fixes #25288

* Use `$component-active-bg`, `$component-active-color` in custom-control-indicators and pagination for checked, indeterminate, and active states

* Button and Forms focus colors should be based on `$component-active-bg`

When using the `media-breakpoint-between` or `media-breakpoint-only`
mixins with a custom breakpoint map – not defined as `$grid-breakpoints`
– the mixin incorrectly defaults back to the global `$grid-breakpoints`
map in certain situations. This commit correctly passes on the
`$breakpoints` argument to the other mixins called within the block.

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

added variable for the background of checked and indeterminate custom inputs and radios that are disabled
added styles for these cases