This CL includes the following changes:
1) Ignore ShouldReduceMemory for MinorMC (since it can't move objects)
2) Make FLAG_page_promotion more explicit in the condition
3) Take wasted bytes into account for MinorMC (full GC can compact and
   "reset" wasted bytes)

Bug: v8:12612
Change-Id: I64d214e692b8ecd20189c59e2a77807f05e43817
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3879606Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83086}