This is a reland of ab7e89f1

Original change's description:
> [TurboProp] Add PendingOperand for use by fast register allocator.
> 
> Adds a pending operand type for use with the fast register allocator.
> These operands chain together multiple operands together, enabling
> the allocator to keep track of multiple pending operands, then
> replace them all with the allocated operand in one go.
> 
> BUG=v8:9684
> 
> Change-Id: I5d8150f3f26549a747a2e89e32e31135e89dff9c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2292302
> Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#69019}

Bug: v8:9684
Change-Id: I60b902be82b766d98c0f08c9394fcac72d3b914a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2315994Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Auto-Submit: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69042}