Move wxTransform2D methods' bodies to geometry.cpp.

Move wxTransform2D methods' bodies to geometry.cpp.

They are all virtual and so cannot be inlined anyway and having them in
the header like this confuses the g++ linker into always pulling some of
the methods in merely because geometry.h was included.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73984 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775