Revision 1862636

Improved: Make ‘FormRenderer#getUsedFields’ more generic
(OFBIZ-11135)

We want to be able to reuse the selection of used fields for any form
renderers. As a consequence it seems more appropriate to move the
behavior of ‘FormRenderer#getUsedFields’ to the ‘ModelFormField’
class.

Additionally we have decoupled the filtering logic from the iteration
process by constructing a stateful predicate.

The corresponding unit tests have been adapted to both changes.