Cleanup of wxDataViewCtrl cell activation code.

Cleanup of wxDataViewCtrl cell activation code.

Fix confusion of what cell activation is and inconsistence with native
handling in GTK+. Document the distinction between activating (~
editing) a cell and activating (double-clicking) the whole item.

Deprecate wxDataViewCustomRenderer::LeftClick() and Activate() methods,
replace them with single ActivateCell() that is called for both kinds of
activation.

Fix implementations so that ActivateCell() is not called on
double-click, when it shouldn't, and vice versa: don't send
wxEVT_COMMAND_DATAVIEW_ITEM_ACTIVATED for cell activation.

Partially reverts r67099 -- restores old 2.9 signatures of compatibility
LeftClick() and Activate() methods.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69473 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775