Activates this, usually by activating the currently focused cell, however some subclasses which embed widgets in the area can also activate a widget if it currently has the focus.
the CellAreaContext in context with the current row data
the Widget that this is rendering on
the size and location of this relative to
the CellRendererState flags for this for this row of data.
if true then only cell renderers that are gtk_cell_renderer_mode_editable will be activated.
Whether this was successfully activated.