UI. Private nested classes should be hidden

[alisevych]

Description

Private nested classes should be hidden from member list.
Currently they are shown and tests can be generated for they non-private methods.

To Reproduce

Steps to reproduce the behavior:

1. IntelliJ IDEA with one of the latest UTBot plugin builds installed.
2. Open/create a Java project
3. Add the following class:

public class A {

    private class Inner {

        private int x;

        public int giveFive() {
            return 5;
        }
    }

    public boolean foo(Inner in) {
        return (in.x > 0);
    }
}

Expected behavior

Private members should not be available for test generation.

Actual behavior

Private class is shown in Member list.
When it is chosen and there are public/package-private methods - tests are generation using reflection.

Visual proofs (screenshots, logs, images)

Environment

IntelliJ IDEA 2022.1.4
UTBot plugin version

Additional context

As discussed with @volivan239 @EgorkaKulikov all public and package-private nested classes are shown in Member list - even if they do not have methods. It is made the same as for case when we display all classes in a package.