Path nodes should be able to edit multiple table rows of vector data

[0HyperCube]

The Path (vector modify) node must store modifications for each shape's element ID now that we support multiple rows of vector data thanks to the work in #1834.

For now, we can do this based on index:

you'd need a HashMap<RowId, VectorDataModification> which would require refactoring all of the tools

(we don't have RowId yet, so we can use usize for its row index instead: HashMap<usize, VectorDataModification>)

In the future, we can attempt a smarter way of generating unique IDs: #1821.

Related: #1929.