Fix validation error when using same id for a parent field and its sub field

Steps to reproduce:

• in a schema, create a complex field "foo" with sub text field "foo"
• place it in a layout
• edit the sub widget configuration (to use a textarea widget for instance)

=> there is a validation error "On creation layout, widget 'Foo' subwidgets, widget 'Foo': bound field type 'complex' does not match the actual field type 'string' for field 'foo' in schema 'testComplexSchema'"