With this change, there are const and mutable version of slices, in
analogy to const and mutable references, which we already have.
A const slice as a readonly view into memory, it doesn't mean that
nobody else has a writable view on it.

An array field in a Torque class produces const slices if it is declared
as const.

Due to limitations in the Torque type system, mutable slices are not
a subtype of const slices of the same type.

Bug: v8:7793
Change-Id: I1ba96e1ee82bf03b5fdc824488981f2a6b5eae8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2560195Reviewed-by: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71481}