replace the frame count unit from the int32_t to float
since animations could smoothly interpolate key-frames.
This notificably improve the animation smoothness in Lottie
Beta API changes:
Result Animation::frame(uint32_t no) -> Result Animation::frame(float no)
uint32_t Animation::curFrame() const -> float Animation::curFrame() const
uint32_t Animation::totalFrame() const -> float Animation::totalFrame() const