upgrade to dart-sass

[liudonghua123]

node-sass ( https://github.com/sass/node-sass ) and libsass ( https://github.com/sass/libsass ) are both deprecated, see more details on https://sass-lang.com/blog/libsass-is-deprecated.

The only active official sass implementation is dart-sass ( https://github.com/sass/dart-sass ). Maybe we should change the implementation from node-sass, libsass to dart-sass, the pure js implementation.

If we use dart-sass, browser support may be easier than none js implementation like less.

[rodneyrehm]

Wouldn't dart-sass flat out replace sass.js? what's sass.js still needed for?

[thoka]

It seems dart-sass still does not run inside the browser ...

sass/dart-sass#25

[thednp]

Hey there. We have the package.json and a dependency list, what would it take more than update to latest version each dependency and build a new sass.sync.js with latest code from libsass?