Switch from grunt-css-url-embed to css-url-embed

This eliminates some rickety indirect dependencies and is a big step
towards removing Grunt.

package.json

@@ -36,6 +36,7 @@
   "devDependencies": {
     "@eslint/eslintrc": "^3.3.1",
     "@eslint/js": "^9.24.0",
+    "css-url-embed": "github:sgravrock/css-url-embed",
     "eslint": "^9.24.0",
     "eslint-plugin-compat": "^6.0.2",
     "glob": "^10.2.3",
@@ -44,7 +45,6 @@
     "grunt-cli": "^1.3.2",
     "grunt-contrib-compress": "^2.0.0",
     "grunt-contrib-concat": "^2.0.0",
-    "grunt-css-url-embed": "^1.11.1",
     "grunt-sass": "^4.0.0",
     "jasmine": "^5.0.0",
     "jasmine-browser-runner": "github:jasmine/jasmine-browser-runner",