Enable DeclarationOrder in scss-lint

What does this MR do?

• Enables DeclarationOrder in scss-lint.
• Fixes all DeclarationOrder violations.
  • @includes - properties violations: 13 (out of 172 (*1))
  • properties - nested rule sets violations: 2 (out of too many cases)
  • @extends - properties violations: 1 (out of 54)
• Fixes a tiny typo in comments in .scss-lint.yml.

Notes

(*1): Counted with the following command:

git grep -B1 '^ *@include' -- app/assets/stylesheets/**/*.scss | grep -c '^--$'

The rule

This rules the order of these 5 declarations as follows:

1. @extend declarations
2. @include declarations without inner @content
3. properties
4. @include declarations with inner @content
5. nested rule sets

Are there points in the code the reviewer needs to double check?

No.

Note: @includes - properties violations ratio is 7.6% (13 out of 172), which may be relatively high.

Why was this MR needed?

To improve SCSS maintainability and consistency.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Part of #23485 (moved)