Release Note: Allow G1 Heap Regions up to 512MB

The JDK-8275056 enhancement extends the maximum allowed heap region size from 32MB to 512MB for the G1 garbage collector.
Default ergonomic heap region size selection is still limited to 32MB regions maximum. Heap region sizes beyond that must be selected manually by using the `-XX:G1HeapRegionSize` command line option.

This can be used to mitigate both inner and outer fragmentation issues with large objects on large heaps.

On very large heaps, using a larger heap region size may also decrease internal region management overhead and increase performance due to larger local allocation buffers.