The clang compiler was running into linker errors constructors of
classes with virtual methods that were inline and destructors that were
not declared at all. In this case, the compiler was not creating
everything needed by a virtual table and the link died.
Also made the TextAnnotation classes conform better to VTK-m coding
style. Specifically, changed the order of words in subclass names (e.g.
TextAnnotationBillboard instead of BillboardTextAnnotation) and broke
out each subclass into its own header/source files.
The template parameters on vtkm::rendering::View are unnecessary. All
three of the templated classes are polymorphic (with virtual functions).
Thus, you just have to specify them at the constructor. Removing the
template parameters makes the syntax a bit cleaner and removes some
unnecessary duplication in the executable.
Removing the template does mean we cannot optimize in the future.
However, I expect us to start using more virtual methods rather than
less, so I think this is a move in the right direction.
The word surface is more often used for something like a polygonal mesh,
so this name is quite confusing. Canvas is consistent with a
conventional name in GUI widget APIs.