This CL types almost all remaining VARIABLEs. Only one remains (in
PrepareValueForWriteToTypedArray) since it depends on a variable
MachineRepresentation. Will be done in a follow-up.

Bug: v8:6949
Change-Id: Icdec3d8fdc1459c0b35fc3d1f7e8816981bbccba
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2282594Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68709}