Add a file input component that works with forms

### Provide a general summary of the feature here

I'm building a form that includes a few sections that require file uploads. It would be nice if I could use the existing form API to handle this scenario. I found [this discussion](https://github.com/adobe/react-spectrum/discussions/5486#discussioncomment-7695236) that covers this topic — has there been any progress made since then? If not, and if there's still interest in implementing this, I'm happy to give it a go.

### 🤔 Expected Behavior?

```tsx

Name




Files



Add

```

### 😯 Current Behavior

The `FileTrigger` component is currently not composable with the `Form` component.

### 💁 Possible Solution

My current best guess is that this would involve:

1. creating a `FormField` component analagous to `TextField` and `NumberField`
2. extending the `Input` component to be composable with `FormField`

I'm unsure how to tackle 2. as the current implementation of file upload in `FileTrigger` doesn't just use ``. Would appreciate any input on this problem!

### 🔦 Context

n/a

### 💻 Examples

_No response_

### 🧢 Your Company/Team

_No response_

### 🕷 Tracking Issue

_No response_

Read the existing Form, FileTrigger, TextField, NumberField, and Input implementations, then review the linked discussion. Determine how file values should participate in form submission and validation; done means a file field composes with Form and the example submits and reports FieldError correctly.

Written by the indexing model from the issue text.