Fuzzer improvements

[Markoutte]

Description

List of changes:

• Randomize fuzzer inputs
• Limit fuzzing attempts
• Mutate primitive values according to comparison operations
• Mutate string constants
• Move fuzz-relative code out of UtBotSymbolicEngine.kt
• Test added

Type of Change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• org.utbot.framework.plugin.api.CombinationsTest
• org.utbot.framework.plugin.api.ModelProviderTest

Manual Scenario

1. Disable engine.traverse() function by commenting it in UtBotTestCaseGenerator:185
2. Build and run
3. Create a function as listed below
4. Run UtBot and check that it creates tests with all branches covered and the tests have names which end with word "FuzzerN"

    public String foo(int a) {
        if (a < -2.0) {
            return "-1";
        }
        if (a > 5) {
            return "-2";
        }
        if (a == 3) {
            return "-3";
        }
        if (4L < a) {
            return "-4";
        }
        return "0";
    }

Checklist:

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• New documentation is provided or existed one is altered
• No new warnings
• Tests that prove my change is effective
• All tests pass locally with my changes

[denis-fokin]

Please, add explanation why the parameters are unused, may be it is worth to introduce a default value.

[denis-fokin]

In my opinion simple is too general term. Could you pick a more specific name? And add some documentation to the class.

[denis-fokin]

even we -> even if we