Break implicit dependency of "core" on "adv" via wxXmlResourceHandlerImplBase.

Break implicit dependency of "core" on "adv" via wxXmlResourceHandlerImplBase.

wxXmlResourceHandlerImplBase::GetAnimation() returned wxAnimation by value
which created references to wxAnimationCtrlNameStr and wxNullAnimation
symbols, defined in the "adv" library, in "core" when using Sun CC even though
they were not referenced directly.

Fix this by returning wxAnimation by pointer to keep it opaque for "core" code.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72782 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775