Support richer `@EnsuresNonNullIf` with methods, at least for library models

[msridhar]

This is important for handling certain JDK cases like Class.isArray(), which if it returns true, ensures that getComponentType() on the same object returns @NonNull:

https://github.com/typetools/jdk/blob/9b1958333ddd472b31fa9ad6cc1b7faf80edd664/src/java.base/share/classes/java/lang/Class.java#L844

Not modeling this leads to a lot of false positives on JUnit (with JSpecify JDK models enabled). There's a similar relationship between Queue.isEmpty() and Queue.peek() / Queue.poll(), though modeling that is more complex since a Queue can contain nulls and also isEmpty() is inherited from Collection.