build(sass): switch from gulp-sass to sass-embedded

[simeonoff]

Closes #13515

Additional information (check all that apply):

• Bug fix
• New functionality
• Documentation
• Demos
• CI/CD

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them

[kdinev]

@simeonoff This is significantly faster! You're helping save the environment! :)

You should propagate the change to 16.0.x and 15.1.x if possible.

[simeonoff]

@simeonoff This is significantly faster! You're helping save the environment! :)

You should propagate the change to 16.0.x and 15.1.x if possible.

Roger, will do.

Can't take all the credit for it as it's mainly the power of sass-embedded being utilized here.