[cleanup][CSA] TNodify VARIABLE to TVARIABLE

There are some changes that stem from this, e.g Bind to =.

Bug: v8:10021
Change-Id: Ia421578de7dce99ba843c2ec96b5e40bf3e2f941
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1993297Reviewed-by: Mythri Alle <mythria@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65688}