[autoform] Avoid two calls to field.process_form for the same field in some cases
when some entity is being created and data include non-inlined relations, the
values for this relation are now stored for later usage, avoiding two calls
to field's process_form method, which may be unexpected for custom fields.
This has been discovered in saem_ref#f5444b1f9770.
Reorganize imports in the test along the way.
### Requirements for tests in various cubicweb/**/test directories. ###
## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest
## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag
## cubicweb/devtools/test
flake8
## cubicweb/hooks/test
psycopg2
## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
## cubicweb/sobject/test
cubicweb-comment