The Torque compiler makes heavy use of scoped globals (contextuals).
This created a problem for the design of the compiler interface:

    - Either the compiler provides all the necessary scopes itself,
      disallowing callers any access to the contextuals, which might
      contain data the caller is interested in (such as the
      compilation result).
    - Or the caller provides all the necessary scopes.

This design was fine when the compiler executable was the only user.
With the recent addition of unit tests and the language server, this
interface became brittle, as missing scopes are only detected at
runtime.

This CL refactors the compiler interface to not leak contextual
scopes past the interface boundary. Content of contextuals is
collected and returned, providing access for the caller and freedom
to either use the data directly or move it into the callers own scopes.

R=sigurds@chromium.org

Bug: v8:7793
Change-Id: Ieb988522d08fc6026b3fb74d976008e566146770
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1529000
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60867}