[GR-68875] Fix class initialization problems.

[graalvmbot]

• Fixed a rare race condition in the class initialization logic, where other threads could see uninitialized values for fields that are written in a static initializer.
• Fixed deadlocks that could occur if OutOfMemoryErrors or StackOverflowErrors happened during class initialization.
• Fixed deadlocks and other problems that could happen if recurring callbacks were executed during certain parts of class initialization.
• Fixed an issue in ClassInitializationInfo.markReached(...) which could prevent types from being marked as reached. Other threads could also see inconsistent reachability states for the class hierarchy.
• Fixed an issue where ClassInitializationInfo.typeReached could be updated from UNTRACKED to REACHED.
• Fixed an issue where ClassInitializationInfo.isInitialized() could return false even though the class initializer was already executed.
• Fixed deadlocks where ClassInitializationInfo.isReentrantInitialization() could wrongly return false for virtual threads.
• Fixed an issue where the field ClassInitializationInfo.hasInitializer could be incorrect for classes for which linking failed at build-time.
• Lots of cleanups.