Initilial implementation of Spring test classes code generation

[sofurihafe]

Description

This PR adds support for necessary test class fields rendering (see InjectMocks, Mock below).
Also, in case of mocks it constructs them in test method (see (when(...))).

@Service
public class OrderService {
    @Autowired
    private OrderRepository orderRepository;

    public List<Order> getOrders() {
        return orderRepository.findAll();
    }
}

public final class OrderServiceTest {
    @InjectMocks
    public OrderService orderService;

    @Mock
    public OrderRepository orderRepositoryMock;

    public AutoCloseable mockitoCloseable;

    @BeforeEach
    public void setUp() {
        mockitoCloseable = openMocks(this);
    }

    @AfterEach
    public void tearDown() throws Exception {
        mockitoCloseable.close();
    }

    @Test
    public void testGetOrders1() {
        (when(orderRepositoryMock.findAll())).thenReturn(((List) null));

        List actual = orderService.getOrders();

        assertNull(actual);
    }
}

Fixes nothing, adds new feature.

How to test

Automated tests

No automated tests are present at this moment.

Manual tests

Tested manually on a third-party Spring project.

[EgorkaKulikov]

Currently crashed on the following method from out sample project:

public List<Order> getOrders(boolean flag) {
        if (flag) {
            return orderRepository.findAll();
        }

        return new ArrayList<>();
    }

Crash reason is:

        // Couldn't generate some tests. List of errors:
        // 
        // 1 occurrences of:
        /* class org.utbot.framework.plugin.api.UtAssembleModel cannot be cast to class org.utbot.framework.plugin.api.UtCompositeModel (org.utbot.framework.plugin.api.UtAssembleModel and
        org.utbot.framework.plugin.api.UtCompositeModel are in unnamed module of loader 'app') */

[Damtev]

Some performance and minor issues

[alisevych]

@sofurihafe @EgorkaKulikov @Damtev
Please do not forget to add/check ctg- and comp labels to the PRs