Make TAB behaviour in wxGrid more configurable.

Make TAB behaviour in wxGrid more configurable.

Allow making TAB/Shift-TAB wrap to the next/previous row or going to the
next/previous control when the cursor is at the end/beginning of the current
row easily.

Also add wxEVT_GRID_TABBING event to allow customizing TAB behaviour even
further.

Update the sample to show the different possible standard behaviours and a
stupid example of a custom one (it would be probably more useful to implement
something a tad more realistic, e.g. tabbing to the next non-empty cell).

Closes #14711.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72672 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775