With non-super loads (receiver == lookup_start_object), we don't hit
the code in AccessorAssembler::GenericPropertyLoad calling
CSA::TryGetOwnProperty if the receiver (the lookup_start_object) is a
SMI.

But with super property loads, if we set up lookup_start_object the
right way, we will hit this code.

The code was assuming receiver is a HeapObject, which is too
restrictive. The receiver is only used for the accessor call, so
it's ok to make the type more generic.

Bug: v8:9237, chromium:1139786
Change-Id: I3167ccfb54a49ac1c401040a6f02fc1f3b98d9d1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2484366Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70647}