Create a ResultSetMapping root node, ensure that the top-level server-side node returns a
collection, and hoist client-side type conversions into the ResultSetMapping. The original
result type (which was removed by removeMappedTypes) is assigned back to the top level.
The immutable state of the phase that can also be accessed by other phases.
Run the phase
Create a structured return value for the client side, based on the
result type (which may contain MappedTypes).
The unique name of the phase