Add support for persisting file folder handle in indexdb for permissions

[delebash]

In your article https://web.dev/browser-fs-access/ you showed a method of persisting access. It would be have this functionality included. TY

[tomayac]

You can do this as described in the main File System Access API article. You can get the required file handle as described below:

const previouslyOpenedBlob = await fileOpen();
// Optional file handle to save back to an existing file.
// This will only work with the File System Access API.
// Get a `FileHandle` from the `handle` property of the `Blob`
// you receive from `fileOpen()` (this is non-standard).
const existingHandle = previouslyOpenedBlob.handle;