We see crashes in the wild that we suspect are caused by these changes.
This is a manual revert because of conflicts.

Revert "[turbofan] Fix incorrect CheckNonEmptyString lowering."
This reverts commit b3b70118.

Revert "[turbofan] Fix incorrect lowering of CheckNonEmptyString."
This reverts commit 57582090.

Revert "[turbofan] Significantly improve ConsString creation performance."
This reverts commit d6a60a0e.

Bug: v8:9147
Change-Id: I262c21e5406a9c4c8ad0e0f995582c5802f0fa1e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1571613Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60919}