Came out of PR review https://github.com/openjdk/jfx/pull/839 for JDK-8235491
Hiding a column should remove cells selected in that column when cell selection is enabled.

There is an issue with cell selection not updated on columns modification - the selection visual is kept on the same column index without changing selectedCells accordingly - technically due to looping across the visibleLeafCells vs. all leaf columns. Might or might not be what ux requires, but the selectedCells must be in sync with the visuals always.

To reproduce (using attached tester):
- create a Tree/TableView with several columns and cell selection enabled
- select a cell in the last column
- hide the last column
- notice that getSelectionModel.getSelectedIndexes() contains index not visibly selected (since it's in a hidden column)