Vendor condition viewhelper not compatible with TYPO3 7.6

[albig]

The viewhelpers IsConsentField and IsElementAllowed are not compatible with TYPO3 7.6. The followin PHP warning is thrown:

#1: PHP Warning: Declaration of EWW\Dpf\ViewHelpers\IsElementAllowedViewHelper::render($condition) should be compatible with TYPO3\CMS\Fluid\Core\ViewHelper\AbstractConditionViewHelper::render() in /app/web/typo3conf/ext/dpf/Classes/ViewHelpers/IsElementAllowedViewHelper.php line 17

As the way TYPO3 7.6 declares condition viewhelper ist not compatible with older TYPO3 versions, we cannot change the viewhelpers itself.

Proposal:

• remove both viewHelpers as both are special replacements of f:if-viewhelper, checking the backend context additionally
• write a simple ViewHelper "typo3Mode" which returns the TYPO3_MODE constant ('FE' or 'BE') to fluid
• use the standard fluid f:if-Viewhelper with a suitable condition ANDed with TYPO3_MODE