Fuzzer uses erased generic types when creating user defined types

[IlyaMuravjov]

Description

Fuzzer uses erased generic types when creating user defined types, for example, in the class below T is always replaced with Object, even when we test acceptStringValueHolder() method which only accepts GenericValueHolder<String>.

public class GenericValueHolder<T> {
    private final T value;
    
    public GenericValueHolder(T value) {
        this.value = value;
    }

    public T getValue() {
        return value;
    }
    
    public static void acceptStringValueHolder(GenericValueHolder<String> genericValueHolder) {}
}

To Reproduce

Run the following unit test.

@Test
fun `fuzzer correctly creates user defined parametrized types`() {
    val seenGenericValueHolders = mutableListOf<GenericValueHolder<*>>()
    var remainingRuns = 100
    runBlockingWithContext {
        runJavaFuzzing(
            TestIdentityPreservingIdGenerator,
            methodUnderTest = GenericValueHolder::class.java.declaredMethods.first { it.name == "acceptStringValueHolder" }.executableId,
            constants = emptyList(),
            names = emptyList(),
        ) { _, _, (genericValueHolder) ->
            seenGenericValueHolders.add(
                ValueConstructor().construct(listOf(genericValueHolder.model)).single().value as GenericValueHolder<*>
            )
            remainingRuns--
            BaseFeedback(Trie.emptyNode(), if (remainingRuns > 0) Control.CONTINUE else Control.STOP)
        }
    }
    val seenStrings = seenGenericValueHolders.mapNotNull { it.value }
    assertNotEquals(emptyList<String>(), seenStrings)
    seenStrings.forEach { assertInstanceOf(String::class.java, it) }
}

Expected behavior

Java Fuzzer is expected to detect Generic type (when it is defined) and generate correct instances of this type.

Actual behavior

Now Java Fuzzer doesn't take generic type into account. It generates only Object instances.

Visual proofs (screenshots, logs, images)

Unexpected type ==> expected: <java.lang.String> but was: <java.lang.Object>
Expected :java.lang.String
Actual   :java.lang.Object
<Click to see difference>

org.opentest4j.AssertionFailedError: Unexpected type ==> expected: <java.lang.String> but was: <java.lang.Object>
	at app//org.junit.jupiter.api.AssertInstanceOf.assertInstanceOf(AssertInstanceOf.java:51)
	at app//org.junit.jupiter.api.AssertInstanceOf.assertInstanceOf(AssertInstanceOf.java:35)
	at app//org.junit.jupiter.api.Assertions.assertInstanceOf(Assertions.java:3539)
	at app//org.utbot.fuzzing.JavaFuzzingTest.fuzzer correctly creates user defined parametrized types(JavaFuzzingTest.kt:325)