TurboFan creates DisallowHeapAccess scopes, to prevent heap access in
the concurrent parts of the compiler. Then, for parts of the compiler
that do want to access the heap, it either creates Allow* scopes (which
should be avoided since they "punch a hole" in the Disallow* scopes), or
relies on a weakening of Handle::IsDereferenceAllowed which allows
handles owned by a LocalHeap to be dereferenced even if there is a
DisallowHeapDereference scope.

This patch:

  a) Strengthens the implicit requirements around handle dereferencing
     to require a running heap on this thread (either main-thread heap
     or an un-parked, un-safepointed LocalHeap).
  b) Removes the overly strict Disallow scopes in TurboFan, relying
     instead on implicit requirements for allocation/handle
     dereferencing in off-thread code.
  c) Cleans up the "should_disallow_heap_access" predicate to be more
     explicit about what should be disallowed (e.g. property accesses
     can't be computed concurrently)

Change-Id: Icb56b7764913ac17e2db197a70bb189af88a6978
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2554617
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71600}