Parameters of native methods should be effectively final

[aosen-xiong]

Get the error from eisop/jdk#122

Take this code:

import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;

public class Demo{
    @EnsuresNonNullIf(expression = { "#1" }, result = true)
    public native void test(Object obj);
}

Error from Nullness Checker:

Demo.java:6: error: [flowexpr.parameter.not.final] parameter obj in 'obj' is not effectively final (i.e., it gets re-assigned)
    public native void test(Object obj);
                       ^
1 error

We should treat the parameters of native method as effective final, like abstract method.