Pin karma and linkinator due to failures

* Bump version to v4.6.0.

* Dist

* Backport #32037

Add `.navbar-nav-scroll` for vertical scrolling of navbar content

* drop the css var for a Sass css

Co-authored-by: Mark Otto <markdotto@gmail.com>

Mention CSP and embedded SVGs in v4 docs

Add a live toast example to the docs

* Backport of changes to v5 docs that updated and clarified information about the Sass compiler used and the minimum rounding precision we recommend with it.

Co-authored-by: Mark Otto <otto@github.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>

Fixes #32474

Improve zip-examples.js by only including the assets we need

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

This is so that it's consistent with the JS workflow thus the cache should match.

* Clarify Sass import and customize docs for how to modify variable defaults

* Add an npm starter project callout to a few pages

They're links, acting as links. Just because they're styled as buttons visually (as is often the case for "Call to action" (CTA) links) doesn't mean they need/get `role="button"`

* `border: none`
* `outline: none`

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

* lowercase `runner.os`
* remove `CI` environment variable since it's already set by the runner

Backport of https://github.com/twbs/bootstrap/pull/32754

Manual backport of https://github.com/twbs/bootstrap/pull/32751 (which has not been merged yet, but assume it will shortly)

Manual backport of https://github.com/twbs/bootstrap/pull/32689

Manual backport of https://github.com/twbs/bootstrap/pull/32631

package.json: move `version_short` variable under the `config` object

This is so that it works on npm 7.x too.

* rename constants
* enforce the constants to be Boolean
* use the coverage plugin only one time, on the latest jQuery run
* fix karma `logLevel`

* @babel/cli                   ^7.12.8  →  ^7.12.10
* @babel/core                  ^7.12.8  →  ^7.12.10
* @babel/preset-env            ^7.12.7  →  ^7.12.11
* @rollup/plugin-babel          ^5.2.1  →    ^5.2.2
* @rollup/plugin-commonjs      ^16.0.0  →   ^17.0.0
* @rollup/plugin-node-resolve  ^10.0.0  →   ^11.0.1
* autoprefixer                 ^10.0.2  →   ^10.2.1
* cross-env                     ^7.0.2  →    ^7.0.3
* eslint                       ^7.14.0  →   ^7.17.0
* eslint-config-xo             ^0.33.1  →   ^0.34.0
* eslint-plugin-unicorn        ^23.0.0  →   ^25.0.1
* find-unused-sass-variables    ^3.0.0  →    ^3.1.0
* hugo-bin                     ^0.66.2  →   ^0.68.0
* linkinator                    ^2.2.2  →   ^2.11.2
* nodemon                       ^2.0.6  →    ^2.0.7
* postcss                      ^8.1.10  →    ^8.2.3
* postcss-cli                   ^8.3.0  →    ^8.3.1
* qunit                        ^2.12.0  →   ^2.13.0
* rollup                 ...

Add two new variables for pagination border-radius values

Docs: Tweak the wording for collapse to indicate button is preferred/more semantic

Clarify the `$enable-shadows` option in our docs

Bump copyright year to 2021

While technically it still works, we're already saying authors shouldn't do it later on, and we removed any examples of this. This was a straggler.

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

Fix popover docs example

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

* CONTRIBUTING: mention dist files

* Update CONTRIBUTING.md

Co-authored-by: Mark Otto <markd.otto@gmail.com>

Co-authored-by: XhmikosR <xhmikosr@gmail.com>