In the process:

* Augment C++-generated Torque classes with SizeFor methods to
  calculate size of instances.

* Add a new "@generateBodyDescriptor" annotation that causes Torque to
  generate C++ BodyDescriptors code that can be used to visit objects
  compatible with existing V8 mechanisms, e.g. GC

* Fully automate C++ macro machinery so that adding non-extern Torque
  class doesn't require any C++ changes, including ensuring generation
  of instance types and proper boilerplate for validators and
  printers.

* Make handling of @export a true annotation, allowing the modifier to
  be used on class declarations.

* Add functionality such that classes with the @export annotation are
  available to be used from C++. Field accessors for exported classes
  are public and factory methods are generated to create instances of
  the objects from C++.

* Change the Torque compiler such that Non-exported classes implicitly
  have the @generateBodyDescriptor annotation added and causes both
  verifiers and printers to be generated.

* Switch non-extern Torque classes from using existing Struct-based
  machinery to being first-class classes that support more existing
  Torque class features.

Change-Id: Ic60e60c2c6bd7acd57f949bce086898ad14a3b03
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2007490
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66621}