Use symbolic constants instead of magic numbers in wxDataViewCtrl code.

No real changes, just add SortColumn_XXX symbolic constants which are somewhat
more clear than -1 and -2 used before. Although the code based on the global
variables remains as bad as before.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73634 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Disable sorting of generic wxDataViewCtrl while it is frozen.

Don't sort the contents of wxDataViewCtrl while it is frozen and resort it
only when it is thawed. This dramatically speeds up adding items to the
control when sorting is used as we only sort it once now instead of doing it
after adding every item.

Closes #14073.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73635 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775