Fix bug in formatting edit values for clashing custom field names.
Fix bug in formatting edit values for clashing custom field names.

Because we were not filtering by both model and field name, but just field
name, `UserDefinedFieldDefinition.clean_value` was being given the
`datatype_dict` of Bioswale.Perennial Plants for an edit on the
Perennial Plants field of a Rain Garden.

Connects to #2366

RickMohr/otm-core,maurizi/otm-core,RickMohr/otm-core,RickMohr/otm-core,RickMohr/otm-core,maurizi/otm-core,maurizi/otm-core,maurizi/otm-core