This allows arbitrary expressions to specify the length of an array.
These expressions get access to globally declared things and the
preceding fields of the current object.
Unfortunately, this breaks generated C++ runtime code, so as a
workaround, I special-case expressions that are just an identifier
and handle them as before. We might want to support more cases there
in the future, probably also with special-casing since having a full
C++ back-end for Torque is infeasible.

Bug: v8:10004 v8:7793

Change-Id: I0d5d1200c0e727766beed7bfb2d43a8abb9cacf0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1942610
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65427}