Feature: Conveniently get adjacent/neighbor cells from/relative to current cell

[vincerubinetti]

I know we can get any arbitrary cell from any cell in the table using existing functions, but it's somewhat verbose, having to pass around indices and lookups. It would get more complicated for other users (not me) that are using the more advanced functionality like merging/spans/grouping/whatever, and the library could perhaps handle these more complex cases.

It'd be cool if we could do something like cell.getRelative(0, -1) to e.g. get the cell in the same column, in the row directly above the current cell. And maybe other things like cell.getRelative(-2, "first"), and equivalent functions for other objects like row.getRelative(1) (one row below this one).

For context, I want to write some general logic that renders cells as ... ellipses when their values are exactly the same as the cells above them. Another example use case could be coloring cells differently based on the contents of adjacent cells.