Deal with synthetic and implicit parameters properly when getting the generic type of a parameter

The logic in ReflectionHelper#typeOf(Executable, int) is incorrect.

Take this example:
method(implicit parameter 1, parameter 2, parameter 3)

When trying to get the generic type of parameter 2 with index 1, it will in fact return the type of parameter 3 as parameterIndex >= genericParameterTypes.length is false and genericParameterTypes only contains [parameter 2, parameter 3] as implicit parameters are ignored by getGenericParameterTypes().

All in all, the algorithm of ReflectionHelper#typeOf(Executable, int) always returned a result but it could be an incorrect type.

This method is not used anymore so let's get rid of it. But the logic was copied in JavaBeanExecutable and it requires fixing there.