Add validators for integer and floating point numbers.
Add an example of their use to the validate sample as well as a new unit test
and documentation for them.
Use the new classes instead of wxTextValidator in wxGrid code.
Closes#12166.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66714 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775