Optimization marker and the optimized code used to share the same slot
in the feedback vector as they were mutually exclusive. With turboprop
we would want to mark the function for tier up to Turbofan while holding
the optimized code for Turboprop. So this cl uses the existing padding
field to hold the optimization marker instead.

As a driveby, removes unused JSFunction::ClearOptimizedCodeSlot function
and fixes a minor bug in Runtime_GetOptimizationStatus.

Bug: v8:9684
Change-Id: I18c551a69648a0837d16c5453d023c0b295b1521
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2467836
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70789}