chore: init frontend-source directory with tooling scaffold

Former-commit-id: 435fb8e3e4f8e334ad3b0e95052edbdd9547d197

frontend-source/scripts/node_modules/@jridgewell/trace-mapping/src/strip-filename.ts

@@ -0,0 +1,8 @@
+/**
+ * Removes everything after the last "/", but leaves the slash.
+ */
+export default function stripFilename(path: string | undefined | null): string {
+  if (!path) return '';
+  const index = path.lastIndexOf('/');
+  return path.slice(0, index + 1);
+}