Changes:
- Fix OpcodeLength for array.copy
- Check that the destination array for array.copy is mutable.

Bug: v8:7748

Change-Id: I2c84b967ba91e150b772a959e76ebb382bfc29bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2928176Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74861}