OOB Asset url asset loading race condition

[tslater]

When OOB assets are loaded over URL, the animation does not wait until the image is downloaded and there is currently now way to know if Rive as completed loading the asset. This means that the image is not visible in the animation and then just pops in when it loads.

Rive should either wait until the image is downloaded in order to initialized and run the animation, or at least give us a loading status so it can be managed in code.

[bassrock]

I've also encountered portions of this with #342

[vileikis]

Same here, I have rive files with up to 10 assets and they randomly appear when animation plays. It will be nice to have onAssetsLoaded and onAssetsLoadingProgress props to gracefully manage this.