Revert doesn't restore binary files after relaunch

[LilithSilver]

Repro:

1. Add binary files
2. Remove binary files
3. Reopen Godot
4. Revert to "Add binary files"
5. The files aren't added

The reason this occurs: DocumentWatcher has not ingested the old, removed binary docs at this stage.

Fix: We must add a method to DocumentWatcher that allows polling/tracking an arbitrary binary doc ID. Then, we need to adjust anything that uses get_linked_file to asynchronously get multiple linked files at a time, and await on that. Possibly a helper method -- get_linked_files.