This CL lets Torque generate the Context C++ class and BodyDescriptor
for Context.
This requires two Torque changes:

- Allow @generateBodyDescriptor on @abstract classes, since all Context
  classes share the same BodyDescriptor.

- Add a new annotation @relaxedWrite, which makes C++ setters
  use WRITE_RELAXED_FIELD instead of WRITE_FIELD.
  Attention: As a side-effect, this CL disables using
    WRITE_RELAXED_FIELD by default for all non-array fields. If this
    causes problems, we should manually add @relaxedWrite to the
    corresponding fields.

Bug: v8:7793

Change-Id: I735b310bcb36a3612d86c22efa9c0bfc108d4ca6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2529453
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71123}