Readonly
destinationSuggested file location to write the new backup.
Note that your extension is free to ignore this and use its own strategy for backup.
If the editor is for a resource from the current workspace, destination
will point to a file inside
ExtensionContext.storagePath
. The parent folder of destination
may not exist, so make sure to created it
before writing the backup to this location.
Additional information used to implement
CustomEditableDocument.backup
.