Change geometry type enum and mark as stable

As mentioned in 9d00b1b9931c113f594582728a91b32f245d948f, the main purpose of this change is to minimize a diff.  Any other justification for changing the enum would be sketchy at best.  If we want consistency we'll have to change a lot more than this enum.

An alternative to this change would be to change the enum in the `vector-api` branch (this would be a far smaller change).  But I'm not going to hold out for that.