Simplify parseTypeReference

[ghost]

Create the node first, rather than creating it later and setting its pos to another node that was created first.

[sandersn]

So pos isn't needed, or does finishNode set the pos based on children's span or something?

[ghost]

pos is set to the current position by default. If we create a node "too late" we may need to set it to an earlier position. But in this case we can create the node at the right point in time.