perf: remove cosmiconfig from postcss-loader (#3063)

packages/core/prebundle.config.mjs

@@ -176,6 +176,13 @@ export default {
         semver: './semver',
       },
       ignoreDts: true,
+      beforeBundle(task) {
+        replaceFileContent(join(task.depPath, 'dist/utils.js'), (content) =>
+          // Rsbuild uses `postcss-load-config` and no need to use `cosmiconfig`.
+          // the ralevent code will never be executed, so we can replace it with an empty object.
+          content.replaceAll('require("cosmiconfig")', '{}'),
+        );
+      },
       afterBundle: writeEmptySemver,
     },
     {