Problem with Arrays in FormData Proxy

This is an issue which is related to #2616.
When trying to add an array of objects, the objects will be represented as `[object Object]`.

What do I want to do?
I want to select one or multiple files.
Then, using `htmx:configRequest`, I want to map the files to their metadata which is sent to my endpoint.

Behavior in HTMX 1.x:

```html

function convertFilesToMetadata(event) {
var files = event.detail.parameters.files;
event.detail.parameters.files = files.map((file) => ({
name: file.name,
size: file.size,
lastModified: file.lastModified,
type: file.type,
}));
}

```

Bug in HTMX 2.x:
```

function convertFilesToMetadata(event) {
var files = event.detail.parameters.files;

if (files.length < 1) {
// cancel event, no files selected
event.preventDefault();
return;
}

// convert files to dictionary of metadata
event.detail.parameters.files = files.map((file) => ({
name: file.name,
size: file.size,
lastModified: file.lastModified,
type: file.type,
}));
}

```

This will return `undefined`, since the `Proxy` does not implement `map`.

Changing map to a simple `for`, will result in the issue of `[object Object]`:

```html

function convertFilesToMetadata(event) {
console.log(event);
var files = event.detail.parameters.files;

if (files.length < 1) {
// cancel event, no files selected
event.preventDefault();
return;
}

var metadata = new Array(files.length);
for (let index = 0; index < files.length; index++) {
let file = files[index];
metadata[index] = {
name: file.name,
size: file.size,
lastModified: file.lastModified,
type: file.type,
}
}
event.detail.parameters.files = metadata;
}

```

Applying, `JSON.stringify` on the object or metadata does not help because then it will be parsed as a string of JSON and not the object itself.
Trying to assigning it directly `event.detail.parameters.files[index]` also does not work.

Other issues/breaking changes:
- A single file is now the file itself and not an array as before in 1.x
- Assigning an array with 1 element to the formData will also unpack the array
- In the other issue #2616, there is also a mention that the `FormData` object can be accesses via `event.detail.formData`, however, upon inspection it will be empty.