This is a reland of 200a594a.
The failing DCHECK was wrong, which is fixed now.

Original change's description:
> [wasm][gc] Reenable discarding system pages
>
> On windows, the range to be discarded needs to be split by the
> reservations, analogous to committing. This CL reuses the same logic,
> and reenables discarding pages on all platforms.
>
> R=mstarzinger@chromium.org
>
> Bug: v8:8217
> Change-Id: I11716d6381f765bdfe4cf48502b5cdc1f42cf8ab
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1611682
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61526}

Bug: v8:8217
No-Try: true
Change-Id: I293c638a5bc4678591a9c02704770ab54af39bdb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1613248
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61530}