Add an action for arithmetic calculations.
This adds an action for arithmetic operations with pre-defined binary arithmetic operators. Operands can be either defined statically in the action's configuration or parameters, the latter overwriting the former, if both are given.
**(Power of) - available since PHP 5.6
This action uses
eval() for performing the calculation. For safety, operands are being validated to be numeric; operators are being validated to be in the list of pre-defined operators.