In 5.1.1.4.29 the signature of the cast function specifies the non-existing return type Edm.Any.
The return type of the cast function is determined by the type parameter of the function, so the correct signature is
type cast(type)
type cast(expression,type)
(as stated by the description "The single parameter cast function returns the current instance cast to the type specified. The two-parameter cast function returns the object referred to by the expression cast to the type specified.")