Update WebOptimizer Sample to stop using SharpScss (libsass is deprecated)

[jzabroski]

Summary

1. libsass is deprecated
2. SharpScss uses libsass
3. WebOptimizer.Sass already exists, and uses LibDartSass for compilation, which is actively supported

Details

From the README.md on libsass:

Warning: LibSass is deprecated. While it will continue to receive maintenance releases indefinitely, there are no plans to add additional features or compatibility with any new CSS or Sass features. Projects that still use it should move onto Dart Sass.

Would you like to submit a PR?

Yes. TBD.

Some thoughts:

1. Can use MSBuild Solution Filters (.slnf) introduced in MSBuild 16.7 to filter out the sample for Sass https://learn.microsoft.com/en-us/visualstudio/msbuild/solution-filters?view=vs-2022
2. This would allow obviating the otherwise circular dependency that would be created.
3. Might make sense to just reference WebOptimizer.Sass as a git submodule. Need to think about this.