- Change the Torque parser to support nested namespaces. All the rest
  of Torque has already supported them for a long time.
- Use nested namespaces in ic-callable.tq and torque-internal.tq.

Bug: v8:7793
Change-Id: I869ce21e4a6aeb5951815815cbd4feedfcb312b3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2196127
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67750}