Translate temp row ids inside RefList values (#2477)

The data engine lets a bundle of user actions use temporary negative row
ids: an add may declare e.g. row id -1, later actions in the same bundle
may refer to -1, and the engine replaces it everywhere with the real id
it assigns. This already worked in Ref values and in row-id positions,
but inside RefList values temp ids landed as literal negatives. Add the
missing ReferenceListColumn.prepare_new_values override, mirroring
ReferenceColumn. Rows that reference each other through RefList columns
can now be created in one bundle, even mutual references within a single
bulk add.