Grid: Screen reader does not speak column header info when shift-tab from data cell

[Becky Gibson]

This is a consequence of fixing #9756 that I thought was related to the browser. It is not a browser issue.

To reproduce tab into a grid. Focus will go to a column header and JAWS 11 will speak the contents of the column header. Tab again to put focus into a data cell. JAWS 11 will speak the contents of the data cell. Shift-tab back to the column header - JAWS does NOT speak the column header contents.

Since focus is not longer directly set on column header cells (see #9756), I need to set focus back to the grid domNode so that the browser will pick up the use of aria-activedescendant to indicate the active column header cell.

[Becky Gibson]

(In [20692]) fixes #10231. Need to set focus onto the grid domNode so the browser can pick up the use of aria-activedescendant to identify the current column header.