These new apis would enable users to easily modify the motion scene,
The data structure of the paints has been changed from an array to a list.
@APIs:
std::list<Paint*>& Canvas::paints() noexcept;
std::list<Paint*>& Scene::paints() noexcept;
@Deprecated:
Result Canvas::reserve(uint32_t size) noexcept;
Result Scene::reserve(uint32_t size) noexcept;
@Issue: https://github.com/thorvg/thorvg/issues/1203
