Fixes#9882 and #9691
In 2.0, we would accept data coming back from an update operation and
then reflect those changes in UI.
However, in 3.0, we did not do that anymore - meaning you could change a
document with hooks in `beforeChange` or `afterChange`, but then not see
the changes made on the server.
This PR updates the way that `mergeServerFormState` works, and adds a
property to optionally allow values from server form state - which can
then be used in the `onSuccess` form handler which may need to define
new field values.
3ea1d393fd