Inline the css-variables-parser dependency (#29571)

Get rid of the `postcss@7` dependency by inlining this simple function.

package-lock.json

@@ -24,7 +24,6 @@
         "chartjs-plugin-zoom": "2.0.1",
         "clippie": "4.0.7",
         "css-loader": "6.10.0",
-        "css-variables-parser": "1.0.1",
         "dayjs": "1.11.10",
         "dropzone": "6.0.0-beta.2",
         "easymde": "2.18.0",
@@ -4032,35 +4031,6 @@
         "node": "^10 || ^12.20.0 || ^14.13.0 || >=15.0.0"
       }
     },
-    "node_modules/css-variables-parser": {
-      "version": "1.0.1",
-      "resolved": "https://registry.npmjs.org/css-variables-parser/-/css-variables-parser-1.0.1.tgz",
-      "integrity": "sha512-GWaqrwGtAWVr/yjjE17iyvbcy+W3voe0vko1/xLCwFeYd3kTLstzUdVH+g5TTXejrtlsb1FS4L9rP6PmeTa8wQ==",
-      "dependencies": {
-        "postcss": "^7.0.36"
-      }
-    },
-    "node_modules/css-variables-parser/node_modules/picocolors": {
-      "version": "0.2.1",
-      "resolved": "https://registry.npmjs.org/picocolors/-/picocolors-0.2.1.tgz",
-      "integrity": "sha512-cMlDqaLEqfSaW8Z7N5Jw+lyIW869EzT73/F5lhtY9cLGoVxSXznfgfXMO0Z5K0o0Q2TkTXq+0KFsdnSe3jDViA=="
-    },
-    "node_modules/css-variables-parser/node_modules/postcss": {
-      "version": "7.0.39",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-7.0.39.tgz",
-      "integrity": "sha512-yioayjNbHn6z1/Bywyb2Y4s3yvDAeXGOyxqD+LnVOinq6Mdmd++SW2wUNVzavyyHxd6+DxzWGIuosg6P1Rj8uA==",
-      "dependencies": {
-        "picocolors": "^0.2.1",
-        "source-map": "^0.6.1"
-      },
-      "engines": {
-        "node": ">=6.0.0"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/postcss/"
-      }
-    },
     "node_modules/css-what": {
       "version": "6.1.0",
       "resolved": "https://registry.npmjs.org/css-what/-/css-what-6.1.0.tgz",