TYPO3 Core

ViewHelpers that do not register "required" as an argument (e.g. `PasswordViewHelper`) pass any value since Fluid v2.12.0 (see https://github.com/TYPO3/Fluid/pull/859).

ViewHelpers that register "required" as an argument (e.g. `TextfieldViewHelper`) interpret the specified value as a bool and if true always render `required="required"` and omit the attribute if false.

Once this registration will be removed, `required="false"` will be passed through as an arbitrary value and rendered in the browser.

While `required="false"` is technically incorrect, browsers correctly interpret the sole existence of the attribute as "is required" no matter which value is set.

Improve the tests to make sure this case is handled correctly once the registration for "required" in the ViewHelpers is removed:
Usage of `required="false"` should be logged as deprecated and simply be removed from the ViewHelper usage.