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

docs/doxygen/overviews/changes_since28.h

@@ -177,10 +177,14 @@ Finally, a few structure fields, notable @c wxCmdLineEntryDesc::shortName,
   available for the scroll target as function of the main window size, please
   see the documentation of this method for more details.
 
-- Signatures of wxDataViewCustomRenderer::Activate(),
-  wxDataViewCustomRenderer::LeftClick() and
-  wxDataViewCustomRenderer::StartDrag() virtual methods changed.  You will need
-  to change them in your derived renderer class too if you override them.
+- Signature of wxDataViewCustomRenderer::StartDrag() virtual method changed.
+  You will need to change it in your derived renderer class too if you override
+  it.
+
+- wxDataViewCustomRenderer::Activate() and
+  wxDataViewCustomRenderer::LeftClick() were replaced with the new
+  wxDataViewCustomRenderer::ActivateCell() method. You will need to change it
+  in your derived renderer class accordingly.
 
 */