Add discarded of memory on memory reducing garbage collections. In
addition, add tracking of discarded memory and properly adjust the
resident memory of heap dumps.

- Memory is discarded during sweeping and the counter is persistent
  across garbage collection cycles.
- Subsequent sweep calls are not supposed to touch the memory anymore.
- As a simplification, discarded memory is tracked on page granularity
  and assumed to be fully paged in as soon as a page's free list entries
  are reused for allocation.

Change-Id: Icfd58f49f3400c4df0d482e20326a0c43c1ca9f5
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3015563
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75677}