feat: replace `@import` with `@use` to fix SASS 2.0 deprecations

[ghiscoding]

• Replace all @imports with @use since this will be removed in dart-sass 2.0, see https://sass-lang.com/blog/import-is-deprecated/
• make changes that are cross-compatible with legacy approach
• it also looks like there's a drop of about 1Kb when zipping the SF vanilla bundle

before changes with @import legacy

after changes with @use modern

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.8%. Comparing base (17cf3e9) to head (0940d10). Report is 4 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1719 +/- ## ======================================== - Coverage 99.8% 99.8% -0.0% ======================================== Files 187 187 Lines 31105 30697 -408 Branches 9763 9763 ======================================== - Hits 31016 30608 -408 Misses 89 89 ```

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