The (now unique)PersistentHandles container follows this path:
  1) PersistentHandles created via PersistentHandlesScope inside of
     CompilationHandleScope
  2) Owned by OptimizedCompilationInfo
  3) Owned by JSHeapBroker
  4) Owned by the broker's LocalHeap
  5) Back to the broker for a brief moment (after tearing down the
    LocalHeap as part of exiting LocalHeapScope)
  6) Back to OptimizedCompilationInfo when exiting the LocalHeapScope.

There is a special case in GenerateCodeForTesting where the JSHeapBroker
will not be retired in that same method. In this case, we need to
re-attach the PersistentHandles container to the JSHeapBroker.

The identity map of the persistent & canonical handles also gets passed
around like the persistent handles. The only difference is that is
created in the CanonicalHandleScope (i.e step 1) is different).

Bug: v8:7790
Change-Id: I2da77a7e08f3fd360a46b606c5fbda08c0af27df
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332811
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69360}