The SSF would correctly filter out readonly fields when saving a
toplevel form, however it could not remove readonly values when saving
o2m pseudo-records to the parent form (as these would be expected to
remain available for reading upon the next edition and whatnot), so
these values would get sent in 0/1 commands.
Filter out these fields during the parent / toplevel save call.
Complexity notes:
* evaluating readonly modifiers requires the entire record, so
unchanged fields still have to be written back to the parent form
and be filtered out when *it* is set up for save, an alternative
would be to store the `changed` and `readonly` flags alongside the
record dict, and have the post-process only override the
pre-computed readonly flag using force_save
* had to fix a test to match the new behaviour, the post-edition
states turns out to be in line with the client's behaviour (or how
it looks anyway)
Fixes#32019
Xavier Morel
ef8df8fb4e