Add PriorPoint2 factor type to SDK

[GearsAD]

Looks exactly the same as PriorPose2:

"{\"label\":\"l1f1\",\"_version\":\"0.18.1\",\"_variableOrderSymbols\":[\"l1\"],\"data\":{\"eliminated\":false,\"potentialused\":false,\"edgeIDs\":[],\"fnc\":{\"Z\":{\"_type\":\"IncrementalInference.PackedFullNormal\",\"mu\":[10.0,30.0],\"cov\":[1.0,0.0,0.0,1.0]}},\"multihypo\":[],\"certainhypo\":[1],\"nullhypo\":0.0,\"solveInProgress\":0,\"inflation\":5.0},\"tags\":[\"FACTOR\"],\"timestamp\":\"2022-03-24T22:06:41.310-05:00\",\"nstime\":\"0\",\"fnctype\":\"PriorPoint2\",\"solvable\":1}"