This is necessary in order to deal with the numbers greater than
wxINT64_MAX that can't be represented in just long long.
It also allows to implement the intuitive handling of minus sign for the
unsigned numbers, i.e. not to accept it in FromString(), unlike the
standard functions which do (and parse -1 as 0xffff...fff).
Also extend the tests to check for more boundary cases.
wxNumberFormatter formats and parses numbers with thousands separators.
Add the class itself as well as documentation and the unit test for it.
See #12166.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66710 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
