To reduce physical memory consumption, discard code pages that are
fully freed.
To determine pages which only become fully free after several freed
wasm code objects, this CL adds a {DisjointAllocationPool} to track all
freed code ({freed_code_space_} in {NativeModule}).

R=mstarzinger@chromium.org

Bug: v8:8217
Change-Id: I22ad92d2c0bd4469e92f0dfd5aec05c03b5a47d6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1594728
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61244}