Changes to reduce committed memory: (dotnet#65367)

* Changes to reduce committed memory:
- Be more careful about estimating what is needed in the future
- Decommit regions that haven't been used in 20 GCs
- Keep regions sorted by decreasing commit size and increasing age
- Insturmentation enhancements

* Address code review feedback:
- optimize add_region_in_descending_order to search backwards if the region to be added is not fully committed
- adjust dprintf levels
- fix formatting issues
- made merge_sort_by_committed_and_age more efficient
- fix comment to use symbolic constant instead of number
- added new helper generation_start_segment_rw