Breaking: #69401 - Adopt ext:form to support the Extbase/ Fluid MVC stack 

See forge#69401

Description 

The postProcessor interface and the mail postProcessor have changed.

Validators and filters have been moved to other folders and both class names and algorithms have changed.

Impact 

Own postProcessors, validators and filters will possibly fail with an error.

Affected Installations 

Installations with own postProcessors, validators and filters.

Migration 

Adopt own postProcessors, validators and filters to comply with the current implementation.