Use undo manager from file browser’s potential field editor

We override undo/redo for the file browser so that ⌘Z / ⇧⌘Z will only undo/redo file browser actions when it’s in the responder chain: b9fafd1495d5e5919b92a4d219beb3c78b09538e

This had the unfortunate side-effect of eclipsing the undo support of descendent views of the file browser, like the field editor used for renaming items.