[BP 7.2.5]- Increase in memory usage during instance close with mvccPurger running on a large instance with high purge ratio

The issue was seen in CBSE-16173.

Problem:

Although purger begins scan if there is no memory pressure (doProceed check). But once scanning starts, it depends on hasMemoryPressure check. With monitor stopped during close, the check is no longer updated. If purger was already active during this and the instance is fairly large with a high purge ratio, there is a possibility that it can continue to run till the completion of the batch - which can bring in a lot of pages and records (~55M pages). Note during close the instance is also no longer under swapper action.