[Form] InputFilter BC Break in 2.2.4

Since `2.2.4` validators and filters on Elements are no longer merged into the applied InputFilter.

This causes a BC break as previously we would rely on the form validators for, say, select values, and only have the required flag in the applied input filter.

Breaking test attached, reverting back to 2.2.2 in our app for now.

Ping @weierophinney @bakura10