We also introduce a subclass of AbstractBytecodeArray to allow access
to the off-heap copy of bytecode array from the bytecode iterator.

Note that not all bytecode iterators have been converted to iterate
the off-heap copy; in particular, bytecode analysis still iterates
the on-heap bytecode array.

Bug: v8:7790
Change-Id: Icc1b0adb5f63d7cfe94286311f64f209067bbfd5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1672931
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62403}