JDK 27 G1/Parallel/Serial GC Changes

JDK 27 introduces approximately 350 garbage collection changes, with roughly half being refactorings and cleanups, while the other half addresses bug fixes and new features. The most significant change is JEP 523, which makes G1 the default garbage collector across all environments, replacing the previous environment-dependent defaults. Additionally, G1 no longer resizes the heap after Full GC based on arbitrary heap free ratio percentages, allowing other sizing heuristics to function more effectively.