bindings: Reduce the size of script_state.h

script_state.h is used in 4,500+ compilation units, and this CL reduces
its estimated pre-processed size from 2.13MB to 0.79MB.

* Move |kV8ContextPerContextDataIndex| from v8_per_context_data.h to
  script_state.h.
  Also, it should not be an enum item.

* Generated binding code doesn't include v8_per_context_data.h by
  default. So we need to include it if necessary.

Bug: 242216
Change-Id: Icb219357585ccb55a8932131473fe0a9b3bc1484
Reviewed-on: https://chromium-review.googlesource.com/1125592
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572538}
29 files changed