This class serves as the base for Animation.
The main purpose of its APIs is to control the animation frames.
Its example will be provided in the upcoming commits.
@APIs:
Result Animation::frame(uint32_t no) noexcept;
Picture* Animation::picture() const noexcept;
uint32_t Animation::curFrame() const noexcept;
uint32_t Animation::totalFrame() const noexcept;
float Animation::duration() const noexcept;
static std::unique_ptr<Animation> Animation::gen() noexcept;
@Issue: https://github.com/thorvg/thorvg/pull/1450
