Add more keys to OPFS

[Elchi3]

This was originally added here: #1033 and it had a bunch of later additions in comments (which then got lost as we migrated to BCD tags).

Compare with the latest draft file: https://github.com/web-platform-dx/web-features/blob/main/features/draft/spec/fs.yml

I'm not sure if the correct way forward here is to use compute_from or to split some of this out to a new feature. Help appreciated.

[captainbrosset]

I think these keys need to go into the file-system-access feature instead.

The File System Access API is more general than OPFS. In a way, OPFS is one implementation of the File System Access API, or rather, one way to use it.

The entry point for OPFS is navigator.storage.getDirectory() which gives you access to a directory where you can then read/write/manipulate directories and files, just like you would with the File System Access API. But this directory is per origin only, and the browser can choose to implement it any way it likes (including without using real files on disk).

File System Access API, in contrast, gives you access to the real files and folders on disk, and therefore multiple origins can access the same files if the user allows it.

I think we need to keep all of the filesystem handle interface stuff in the more general File System Access API feature, and leave OPFS mostly focused on the getDirectory method.