* Migrate to use the new Sass JS API by default

Keep the legacy API around, since its removal is still probably a
while from now.

Fixes #837

* Update README for the next major version

Add a migration section, link to relevant Sass documentation, and
add a section about still using the legacy API.

* Update tests to support the new API, sass-embedded

* Prepare changelog entry for the next major version

* Update CHANGELOG.md

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Co-authored-by: Michael Mifsud <xzyfer@gmail.com>

The version of node-sass we depend on only supports up to Node 17

* Silence import deprecation warning while node-sass is supported

* fix: convert to same sourcemap format as gulp-sass v5

Default to relative paths in the sources array.

* test: fix timing issue of rimraf that broke tests on Windows

* chore: upgrade rimraf to a version more stable on Windows

Drop testing on Node 12

* test: move deletion to before, debugging a timing issue on CI