Add Proxy support for JPF on Java 11

[quadhier]

This patch adds Proxy support for JPF on Java 11 and some unit tests. It should fix the following two failing unit tests, which are parts of #274.

gov.nasa.jpf.test.vm.reflection.ProxyTest::testAnnoProxy
gov.nasa.jpf.test.vm.reflection.ProxyTest::testBasicProxy

I have tested locally and found that it fixes these two test cases with no more regressions (7 failing tests left now).

Problem Analysis

In OpenJDK 11, Proxy.newInstance() involves too much code that JPF currently does not fully support; we need to add a model class for java.lang.reflect.Proxy and use JPF's way to implement a simpler one but with the same functionality.

Basic Idea

According to doc of getProxyClass(), a Proxy is defined by its classloader and the List of interfaces to implement (the order is important). But in fact, a Proxy's implementation is solely defined by the List of interfaces it implements (which can be evident by the signature of JDK's proxy generation method ProxyGenerator.generateProxyClass(final String name, Class<?>[] interfaces, int accessFlags)).

We can use the List of interfaces to get a unique name of a Proxy class, then use JDK's ProxyGenerator.generateProxyClass to generate the classfile of it (and cache it in the resolvedClasses), and finally define the class.

Discussions

Why do these two tests pass on master branch (on OpenJDK 8)?

In OpenJDK 8's implementation, Proxy.newProxyInstance() doesn't involve that much code which JPF cannot handle. All we need to do is to implement the native method Proxy.defineClass0().

[cyrille-artho]

Please see my comments. For the first one, we need to create an issue (and have some discussions), so we cannot resolve that right away.

[quadhier]

Please see my comments. For the first one, we need to create an issue (and have some discussions), so we cannot resolve that right away.

Ok, thanks for your reviews @cyrille-artho !

[cyrille-artho]

Great, thank you for your work and updating the tests! I will merge the PR now.