PCScan: Allow non-scannable partitions to have quarantine

If PCScan is enabled via the finch flag, non-scannable partitions must
also have quarantine enabled, since there can be inter-partition
pointers. The CL achieves it by splitting the scannable option in two:
quarantinable and scannable.

Inter-partition pointers have not been a problem for the browser
configuration, since there are only two (scannable) partitions. The CL
is a prerequisite for the optimization that will move data-only objects
into a separate (non-scannable) partition.

Bug: 11297512
Change-Id: I4b9256992a168c79a72f636eb869fc5d235762f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2676183


Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#851132}