Support mock strategies and type replacement in Spring unit test fuzzing

[IlyaMuravjov]

Description

Makes fuzzing in Spring unit tests respect mock strategy and type replacement:

• All types are replaced according to selected Spring configuration before they are passed to actual value providers.
• MockValueProvider is used if mock strategy allows it and type isn't replaced, otherwise ObjectValueProvider is used (MockValueProvider is also used when no other way to create non-null value is found)
• InjectMockValueProvider (one that outputs composite models) is only used to create thisInstance.

How to test

Manual tests

Generate unit tests with every mocking strategy (including Spring-specific mocking strategy that uses Spring configuration) for spring-boot-testing project.

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.

[Damtev]

@Markoutte, could you take a look, please?

[Markoutte]

For me it is hard to understand all type hierarchy in Spring module and all those wrappers, delegators and adapters. Maybe, documentation could help?

[Markoutte]

Marker interface usually doesn't extend any other interfaces and has no methods. This is because you could use several marker interfaces for one class. In this case AnyObjectValueProvider is used as real type in hierarchy, that maybe useful, but I think it is redundant.

[IlyaMuravjov]

It's not redundant, because it's used in MockingJavaFuzzingContext, which avoids mocking types that have value providers other than AnyObjectValueProvider, because it's a bad practice to mock types like List, Date, and Map.

I can't simply list all implementers of AnyObjectValueProvider in MockingJavaFuzzingContext, because the set of these implementers is subject to change as #2583 shows.

Made AnyObjectValueProvider truly a marker interface that doesn't extend any interfaces.