Better sizing in wxDataViewSpinRenderer and wxDataViewChoiceRenderer.

Better sizing in wxDataViewSpinRenderer and wxDataViewChoiceRenderer.

Their GetSize() method used hardcoded size of (80,16). Instead, use
GetTextExtent() to compute the size from content, as should be done. Add
some extra room for editor control's extra parts. The space needed isn't
computed exactly, as that would be quite convoluted (and in the end,
most likely not 100% accurate even then), using a simple approximation
instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68242 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775