Function interp_has_method 

fn interp_has_method(
    _args: &[RValue],
    _named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Check if a method exists for an S4 generic.

@param f character: generic function name @param signature character: method signature @return logical @namespace methods