Fixes #67776

Should make it easier to see what it's doing and debugging failures.

This reverts commit 02d267c5.

Replaces many loops of the form:

```js
for (let i = 0; i < elements.length; ++i) {
    const i = elements[i];
   ...
}
```

with:

```js
for (const element of elements) {
    ...
}
```

Mix of a horrible regex based find/replace and manual touch ups

Happy new year! 🎆

Fixes #62580

+Simplifies the build process.
+Avoids creating a new shell that simply spawns another shell environment.
+Simplifies the update mechanism by removing the need to track the existence of snapUpdate.sh.
+Keeps the logic for snapUpdate.sh close to updateService.snap.ts