This is part 3 of Torquifying DescriptorArray: making it possible to use
the "descriptors" indexed field from code written in Torque. A small
macro EnsureArrayLengthWritable is converted to demonstrate the new
functionality.

This CL also introduces the arrow token `->` and desugars a->b to (*a).b
so that the new builtin looks a little cleaner.

Bug: v8:7793
Change-Id: I84eaa97f664aa67273866760e6ede4346a3ee2f9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1900332
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65046}