Fix Sass compilation when `$color-mode-type` is set to `media-query`

Description

As a summary, this PR fixes Sass compilation when $color-mode-type is set to media-query.

First error

So the first error mentioned in the issue was the following:

Compilation Error
Error: Declarations may only be used within style rules.
    ╷
135 │     --#{$prefix}body-color: #{$body-color-dark};
    │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ╵
  c:\wamp64\www\f3-5\node_modules\bootstrap\scss\_root.scss 135:5             @content
  c:\wamp64\www\f3-5\node_modules\bootstrap\scss\mixins\_color-mode.scss 5:7  color-mode()
  c:\wamp64\www\f3-5\node_modules\bootstrap\scss\_root.scss 133:3             @import
  c:\wamp64\www\f3-5\src\scss\style.scss 25:9                                 root stylesheet
--------------------

The main reason is that we had in _root.scss:

@if $enable-dark-mode {
  @include color-mode(dark, true) {
     --#{$prefix}whatever: #{$whatever};
  }
}

So when we set $color-mode-type to media-query we end up with a generated CSS for this part without any scope!

I haven't found a better way for now to fix it so I've modified our color-mode mixin to:

• Remove the second parameter since $color-mode-type is available globally even within the mixin
• Add a new second parameter to handle this specific use case where we want to add the :root scope

Second and third errors

After having fixed this one, another type of error popped out (I don't have it, I forgot to register it) but that said that it's not possible to use @extend within @media. So our @extend in close button and carousels didn't work. Instead of using @extend I've found a way (maybe not ideal) to replace it with a mixin.

I kept the test() and test2() just for you to spot easily how it works, and also because I haven't found the proper wording :)

Type of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• All new and existing tests passed

Live previews

• https://deploy-preview-37687--twbs-bootstrap.netlify.app/

⚠️ Big warning regarding non-regression testing. It seems to still work for $color-media-type set to data and I tried within the doc to play with the media-query but our doc is not really very usable when we enable the media-query as is; so it was complicated to ensure that it works correctly. I might need someone to double check if it is OK 🙏

Related issues

Closes #37673 (closed)