customRowRender should give selected columns as argument

## Expected Behavior

When using customRowRender, it should be possible to ascertain which columns are currently displayed in the table. Currently, the information given to customRowRender contains data for all the columns in the table, regardless of whether all are displayed. I think it would make sense if 1. the "data" argument only contains data for the currently selected columns (other columns are still accessible through dataIndex) or 2. an additional argument is given that yields the currently selected columns.
If there is a workaround for this, I would happy to hear about it.

My use case is developing draggable rows.

For reference:
Override default row rendering with custom function. `customRowRender(data, dataIndex, rowIndex) => React Component`

Begin with the customRowRender(data, dataIndex, rowIndex) entry point and review how its arguments represent table data and displayed columns. The work is complete when custom row rendering can determine which columns are currently selected while retaining access to other column data through dataIndex.

Written by the indexing model from the issue text.