Use Method::getParameterCount where possible

[stsypanov]

We often use Method.getParameterTypes() which clones underlying array:

@Override
public Class<?>[] getParameterTypes() {
    return parameterTypes.clone();
}

The problem is that array is often used only to get its length, so we allocate memory mostly in vain.

Instead in numerous cases we call Method.getParameterCount introduced in Java 8:

public int getParameterCount() { return parameterTypes.length; }

which doesn't allocate.

In cases where we still need parameter types we can postpone retrieving it until it becomes inevitable.