[svg-native] Spec uses "deleted", "removed" and "forbidden" interchangeably

[litherum]

@AmeliaBR offered the great suggestion to, rather than list deltas from the original spec, list features that are either supported or not supported. So rather than saying things like "chapter is deleted" instead it should say something like "all text facilities are not supported."

It also needs to be cleaned up so that terms are more consistent and clear. If "forbidden" means "the entire document fails to render at all," then nothing in the entire spec should be forbidden. Instead, things that aren't supported should be ignored.

[svgeesus]

I agree that ignored is better than "must halt and catch fire". Ignored could also be clarified. For attributes, behaves as if the attribute was not preset. For elements, the element, its attributes, and all children of the element are treated as if they were not present.

That definition also, by the way, allows document metadata to be specified (because it will be ignored, and not affect rendering)