[web/formfields] Make CompoundField inherit needs_multipart from its subfields If there's a FileField within a CompoundField, the latter will not have the enctype multipart set, even though the FileField needs it. CompoundField should inspect its children fields to determine whether it needs multipart. Closes #3406930.

[wsgi/handler] fix api change from 3.18

[req] deprecate get_cache (closes #3181499)