Convert sets to arrays prior to using spread operator to enable transpilation to ES5 (#3297)

packages/@uppy/core/src/Uppy.js

@@ -1611,9 +1611,9 @@ class Uppy {
     const restoreStep = currentUpload.step || 0
 
     const steps = [
-      ...this.#preProcessors,
-      ...this.#uploaders,
-      ...this.#postProcessors,
+      ...Array.from(this.#preProcessors),
+      ...Array.from(this.#uploaders),
+      ...Array.from(this.#postProcessors),
     ]
     try {
       for (let step = restoreStep; step < steps.length; step++) {