ReadonlyVector3
ReadonlyVector3 =
Readonly<Pick<Vector3,"x"|"y"|"z"|"isVector3"|"clone"|"length"|"lengthSq"|"manhattanLength"|"distanceTo"|"distanceToSquared"|"manhattanDistanceTo"|"dot"|"angleTo"|"equals"|"toArray">>
A Vector3 a reader cannot change: its fields read-only, and only its
methods that write nothing. Three’s methods that take a vector, such as
copy and distanceTo, take this one.