Reland "[dawn][wire] Handle command chunking in the wire in more robustly."

The new assertion added is too strict for the fuzzer, so removes it.
Note that we already handled the case, I just thought that it would be
ok to assert as well, but that causes the fuzzer to crash which is
undesirable.

This is a reland of commit 11b115b26569c8aa46781b4dac589ce17f5d6c89

Original change's description:
> [dawn][wire] Handle command chunking in the wire in more robustly.
>
> - With the changes to make the wire more spontaneous, chunked
>   command serialization and handling need to be updated to work
>   in a multithreaded manner. Previously, the handler assumes that
>   once a chunked command is received, it will receive the entire
>   chunked command before it receives any other commands. This may
>   no longer be true, so we upgrade chunked commands into its own
>   command so with unique id's to ensure that we handle them
>   appropriately.
> - This change also unifies the command id enums in the wire to a
>   single enum since chunked command handling may occur on both
>   the server and the client (though in practice in Chromium,
>   only the server->client may be multithreaded for now.) This
>   allows us to handle commands in a unified way and also ensures
>   that the command ids are now unique both direction.
>
> Bug: 412761856
> Change-Id: Ia1eb34d57c2e2fe0457c70aae9348bc051fce573
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/266475
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Commit-Queue: Loko Kung <lokokung@google.com>

Bug: b:412761856 b:452575709
Change-Id: Ie9c6554908597362cc2576182e09bf49fc35a4b9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/267295
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>