Improve ensureArray and use it in tracing (#8785)

* Improve ensureArray and use it in tracing

* Fix typing

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

src/common/ensure-array.ts

@@ -1,6 +1,8 @@
-export const ensureArray = (value?: any) => {
-  if (!value || Array.isArray(value)) {
+export function ensureArray(value: undefined): undefined;
+export function ensureArray<T>(value: T | T[]): T[];
+export function ensureArray(value) {
+  if (value === undefined || Array.isArray(value)) {
     return value;
   }
   return [value];
-};
+}