Improve UtModel construction

[IlyaMuravjov]

Description

• Fixes Incorrect cast of EmptyMap to LinkedHashMap detected in runtime only #2499
• Introduces construction of assemble models for dynamic proxies to avoid exceptions like java.lang.ClassNotFoundException: jdk.proxy3.$Proxy184 during code generation

How to test

Manual tests

Generate integration tests for all methods in the following class.

@Service
public class Examples {
    public interface SomeInterface {}
    public class SomeInvocationHandler implements InvocationHandler {
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {
            return method.invoke(this, args);
        }
    }

    public SomeInterface proxy() {
         return (SomeInterface) Proxy.newProxyInstance(
            this.getClass().getClassLoader(),
            new Class[]{ SomeInterface.class },
            new SomeInvocationHandler()
        );
    }

    public Map<String, String> emptyMap() {
        return Collections.emptyMap();
    }

    public static class MyTreeMap extends TreeMap<String, String> {
        public MyTreeMap() {
            super();
            put("key1", "value1");
            put("key2", "value2");
        }
    }

    public Map<String, String> myTreeMap1() {
        return new MyTreeMap();
    }

    public MyTreeMap myTreeMap2() {
        return new MyTreeMap();
    }
}

Self-check list

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.