build: avoid installing node-sass (#22283)

We no longer use `node-sass`, but we were still installing it, because `gulp-sass`
depends upon it. These changes switch to a fork of `gulp-sass` that depends on
the Dart version of Sass.

Author: crisbeto

package.json

@@ -172,7 +172,7 @@
     "glob": "^7.1.2",
     "gulp": "^4.0.2",
     "gulp-cli": "^2.3.0",
-    "gulp-sass": "^4.0.2",
+    "gulp-dart-sass": "^1.0.2",
     "highlight.js": "^10.4.0",
     "husky": "5.1.3",
     "inquirer": "^8.0.0",

tools/package-tools/gulp/build-scss-pipeline.ts

@@ -3,14 +3,11 @@ import {join} from 'path';
 import {buildConfig} from '../build-config';
 
 // These imports lack of type definitions.
-const gulpSass = require('gulp-sass');
+const gulpSass = require('gulp-dart-sass');
 const sass = require('sass');
+const sassIncludePaths = [join(buildConfig.projectDir, 'node_modules/')];
 
-const sassIncludePaths = [
-  join(buildConfig.projectDir, 'node_modules/')
-];
-
-// Set the compiler to our version of `sass`, rather than the one that `gulp-sass` depends on.
+// Set the compiler to our version of `sass`, rather than the one that `gulp-dart-sass` depends on.
 gulpSass.compiler = sass;
 
 /** Create a gulp task that builds SCSS files. */