Activate cells from keyboard too in generic wxDataViewCtrl.

Activate cells from keyboard too in generic wxDataViewCtrl.

wxDataViewCtrl only called WXOnActivate() in reaction to double-click.
When Enter/Spacebar was pressed, only
wxEVT_COMMAND_DATAVIEW_ITEM_ACTIVATED was sent, without calling
OnActivate() even if it was possible.

Fixed to handle both kinds of input identically.

Because there's currently no way to change current focus to a particular
column (as GtkTreeView can do), call WXOnActivate() on the first
activatable column.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68952 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775