Fix zoom to dynamic geometry

[ggetz]

Fixes #6269

Moved raising the postRender event to after the frameState.afterRender functions are all called, which means the primitives are once again being marked as ready in time for the viewer to get the boundingSpheres to zoom to.

Double checked throughout the code base, and Viewer._afterRender was the only Cesium after render function which depended on the frameState.afterRender functions being called first.

[cesium-concierge]

@ggetz, thanks for the pull request! Maintainers, we have a signed CLA from @ggetz, so you can review this at any time.

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[hpinkos]

Thanks @ggetz!