The TryGetOwnProperty code supports only unique names that are not
array indices. Unfortunately, this is neither obvious from its type,
nor from its comment, nor from its code.

ProxiesCodeStubAssembler::CheckHasTrapResult violated the assumption
and was already fixed a few days ago. This CL fixes
CheckGetSetTrapResult and improves our code documentation in the
form of comments and assertions. Concretely:

- Add CodeStubAssembler::IsUniqueName and IsUniqueNameNoIndex
- Use IsUniqueNameNoIndex in CheckGetSetTrapResult to guard
  TryGetOwnProperty (bailout to runtime if not satisfied).
- Similarly, use IsUniqueNameNoIndex to simplify the previous fix in
  CheckHasTrapResult.
- Add a IsUniqueNameNoIndex CSA_ASSERT to TryGetOwnProperty and a few
  other places to avoid such bugs in the future.
- Add a IsUniqueName CSA_ASSERT to a few places where we apparently
  expect unique names (I don't know if those allow indices or not).
- Add a DCHECK to Name::IsUniqueName to ensure and document that this
  shortcut version is equivalent to HeapObject::IsUniqueName.

Bug: chromium:937618
Change-Id: Id4a18ab2a0e9c7591b087dd0c9fe018aa9b9ef3a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1514732
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60196}