Add wxDataViewCtrl::SetRowHeight() and provide its generic implementation.

Allow changing the (fixed) row height without using wxDV_VARIABLE_LINE_HEIGHT
which may slow down the control display too much.

The new method is not implemented for the native GTK and OS X implementations
yet but should be simple to implement there.

See #12749.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67885 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775