Port reporting users from CoffeeScript to TypeScript

app/javascript/retrospring/features/user/report.ts

@@ -0,0 +1,6 @@
+export function userReportHandler(event: Event): void {
+  event.preventDefault();
+  const button: HTMLButtonElement = event.target as HTMLButtonElement;
+
+  window['reportDialog']('user', button.dataset.target);
+}