This patch introduces a new LocalIsolate and LocalFactory, which use
LocalHeap and replace OffThreadIsolate and OffThreadFactory. This allows
us to remove those classes, as well as the related OffThreadSpace,
OffThreadLargeObjectSpace, OffThreadHeap, and OffThreadTransferHandle.
OffThreadLogger becomes LocalLogger.

LocalHeap behaves more like Heap than OffThreadHeap did, so this allows
us to additionally remove the concept of "Finish" and "Publish" that the
OffThreadIsolate had, and allows us to internalize strings directly with
the newly-concurrent string table (where the implementation can now move
to FactoryBase).

This patch also removes the off-thread support from the deserializer
entirely, as well as removing the LocalIsolateWrapper which allowed
run-time distinction between Isolate and OffThreadIsolate. LocalHeap
doesn't support the reservation model used by the deserializer, and we
will likely move the deserializer to use LocalIsolate unconditionally
once we figure out the details of how to do this.

Bug: chromium:1011762

Change-Id: I1a1a0a72952b19a8a4c167c11a863c153a1252fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2315990
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69397}

Although AccessorInfos are technically mutable, in practice they are not
mutated after initialization, and they are guaranteed to be immortal and
immovable. So, we can safely make them accessible from the off-thread
factory, as long as the user promises to not try to mutate them. This is
necessary for off-thread class boilerplate creation.

Bug: v8:10218
Bug: chromium:1011762
Change-Id: Id3108a2324a000ea0616b472dd77aed65b1f908e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2080351
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66563}

Remove OffThreadHandle, HandleOrOffThreadHandle, and HandleFor, and
make the OffThreadIsolate allocate "real" Handles. Rather than using
the main-thread Isolate's handle scopes, these off-thread Handles are
backed by a Zone, which is tied to the lifetime of the nearest
OffThreadHandleScope. Eventually, we'll likely want to merge the
implementation of OffThreadHandleScope and HandleScope, but currently
the latter is too tightly coupled to the main thread to do so.

Bug: chromium:1011762
Change-Id: I2a6361931fe3f90a7bef4cc28ee42155fa8d062f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2071865Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66516}

Add off-thread support for literals, including object/array boilerplates.
Notably, this includes adding FixedArray and HeapNumber support to
OffThreadFactory.

As a drive-by, OffThreadHandle is redefined to store an Address rather
than an Object, similar to Handle, so that it still works with forward
definitions of types.

Bug: chromium:1011762
Change-Id: I7c8452f450d8c57fe683a9e44532ce5647c84a11
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036084
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66156}

Add support for internalizing an AstValueFactory using the off-thread
factory. Includes adding ConsString support to OffThreadFactory.

This introduces a Handle union wrapper, which is used in locations that
can store a Handle or an OffThreadHandle. This is used in this patch for
the internalized "string" field of AST strings, and will be able to be
used for other similar fields in other classes (e.g. the ScopeInfo
handle in Scope, object boilerplate descriptor handles, the inferred
name handle on FunctionLiterals, etc.). It has a Factory-templated
getter which returns the appropriate handle for the factory, and a
debug-only tag to make sure the right getter is used at runtime. This
union wrapper currently decomposes implicitly to a Handle if the getter
is not called, to minimise code changes, but this implicit conversion
will likely be removed for clarity.

Bug: chromium:1011762
Change-Id: I5dd3a7bbdc483b66f5ff687e0079c545b636dc13
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1993971
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65816}