FileTransfer.downloadFile should make response headers available to JS

## Feature Request

### Plugin

`FileTransfer` plugin

### Description

After downloading a file, I need to access certain information about it from the response headers.
Currently, the response object is created like this (on Android):

```kt
val response = JSObject().apply {
put("path", filePath)
}
call.resolve(response)
```

in the same scope, a `Map>?` is accessible via `result.data.headers`, which I would like the response object to contain.

### Platform(s)

Android, iOS

### Preferred Solution

Add a `headers` member to the response object of `downloadFile`, which contains the response headers.

### Alternatives

N/A

### Additional Context

N/A