Make scene.freezeActiveMeshes much more usable

[brunobg]

@JCPalmer

Having a higher level can also allow the burial of all these detailed optimizations, but if people had code to do it themselves, it would still work.

Hijacking this quote just to help my point here Post-mortem analysis of a Babylon project

@JCPalmer’s idea seem like the kind of thing that could benefit from higher level hints on the meshes themselves.