Event for model fully renderable

[mkeblx]

A developer will often want to only have a model displayed to the user if it is fully renderable with textures loaded.

Currently we have the ready event fired at an earlier point of the loading process, without a way to tell when the model is more 'ready' with textures loaded. Below is a video of a current implementation with black materials displayed until the textures are rendered.

https://github.com/user-attachments/assets/71187441-1c57-4f7a-ae9f-9f59f1c654f1

Should we have another event for when the model is fully renderable, or, some way for a developer to control the precondition(s) for when the model is rendered?

Related: https://github.com/immersive-web/model-element/issues/75

[mkeblx]

/agenda