Each LHS expression that contains an optional chain of some form is
wrapped in an OptionalChain node. This root node allows us to use a
single jump location for every individual item in the chain,
improving the performance and simplifying the implementation.

Bug: v8:9553
Change-Id: I678563928b2dbfd6200bff55801919d4fd816962
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1723359
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63120}