Add new icons set - CoreUI Icons

- Closes #30796

Switch links to the GitHub organization and fix redirected links

Remove https://glyph.smarticons.co/ from list of suggestions.
The domain is now for sale and is triggers warnings in Firefox and Chrome

* Prep for v4.3.0

* More updates for v4.3.0.

* rerun to build docs source map

- Move 4.1 docs to 4.2
- Update versions everywhere to 4.1.3 with release script
- Manually bump the shorthand version in package.json
- Add 4.2 to the versions docs page
- Update some redirects
- Fix tests asset URLs
- Bump Nuget and more

The SSL certificate of the useiconic.com is expired

With the current docs directory setup, I'm making too many mistakes and have to manually address path changes and directory moves on deploy. This makes for a frustrating experience developing locally and shipping releases. With this PR, we're basically back to the same setup from v3—duplicating the dist directory into our docs directory. Not the most ideal, but very straightforward for me as the release manager.

saves a redirect

* update docs path from docs/4.0/ to docs/4.1/

* bump version to 4.1.0

* Update redirects to work for 4.1 docs move

* Update docs version switcher to include latest and link to 4.0 docs

* re-run dist

* Update package-lock.json

* Update docs-navbar.html

[Icons8](https://icons8.com/) is a great resource for icons.

They provide 15 different icon styles, exportable as fonts or svg

The download link for Entypo (on its website) is invalid. It's a Dropbox link which now results in a 403 error. The website was last updated in 2015 (as seen in the footer).

Feather link didn't go anywhere.

Changed feather link from `colebemis.com/feather` to `feathericons.com`

[ci skip]

- Simpler main nav on all pages
- Back to purple masthead on homepage instead of dark graphite
- Active link styles on the main nav
- Cleaned up sidebar nav
- New docs layout name
- Homepage copy edits
- Updated bright purple docs color