Drop node-sass support

[julien-deramond]

Warning

This PR is heavily draft. It prepares the modifications for when we'll drop node-sass support

Description

This PR drops node-sass support.
Thanks to this drop, we can also make modifications to remove the deprecation warning from the recent Dart Sass versions.

Sub-tasks

• Drop dedicated node-sass GitHub workflow
• Replace RGBA with rgba
• Bump sass → 1.79.x
  • Deprecation Warning: blue() is deprecated. Suggestion: color.channel($color, "blue", $space: rgb) More info: https://sass-lang.com/d/color-functions (same thing for red() and green()) → 1816145
• Bump sass → 1.80.x
• Bump sass → 1.81.x
• Bump sass → 1.82.x
• Bump sass → 1.83.x

• Check the diff between dist/css/bootstrap.css from the main branch and this one

• Check if we need to do something about rfs repository (and vendor dir here)

• Hugo documentation build

  The transpiler to use, either libsass (default) or dartsass
  See https://gohugo.io/hugo-pipes/transpile-sass-to-css/#dart-sass

  See also TESTING Docs: switch to dart sass #39700

  • Make it work locally (macOS)
  • Make it work with Netlify

• Check the documentation to remove node-sass specific content (if any)

• Add somewhere in the documentation that Bootstrap doesn't support node-sass anymore

• After the merge of this PR, update the examples repository

Type of changes

• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• (N/A) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-41112--twbs-bootstrap.netlify.app/

Related issues

Closes #40962
Closes #40849

[julien-deramond]

I removed the mix($indigo, $blue, 50%) because color.mix($indigo, $blue, 50%) doesn't return a value as an hex string, but a color that should be transformed to a hex string. I don't think it's necessary to add such complexity for now. Let's see at the end of the PR if we reintroduce something like that.

[Ayushch-2800]

I think that the mix($indigo, $blue, 50%) is not appropriate in this as css and bootstrap has feature of colour-mix which include the change or mix in colour using hex string but you can't use colour.mix to change colour into hex string

[julien-deramond]

I had to change the path because, otherwise, hugo (via the npm command) will use the sass binary installed from our package.json that doesn't support sass --embedded -> sass --embedded is unavailable in pure JS mode..
Following https://gohugo.io/functions/resources/tocss/#dart-sass, I've installed on my computer sass that supports sass --embedded so the script must use this version instead of the one in node_modules/.bin.
This temp solution makes it work when running npm run docs and npm run start locally on macOS after having installed globally sass with brew install sass/sass/sass.

If there's no other solution, we might need to modify the contributing guidelines to add this extra step and link to https://gohugo.io/functions/resources/tocss/#installing-in-a-development-environment