Allow utilities to preload libraries before sandbox lockdown

Some utilities on Windows wrap dynamic libraries which might be
distributed as components. Allowing these to load requires punching
holes in the sandbox using file interceptions that are being phased
out.

This CL introduces a mechanism for service processes to specify a
list of dll paths which will be loaded before the sandbox goes into
lockdown. They can later be loaded by code using the same path, as
Windows keeps them in memory.

The mechanism uses a new opaque data transfer mechanism in the
sandbox which will extend to different uses later. For
now the list of DLLs is the only data transferred so this CL uses
base::Pickle to serialize & transfer the DLLs to load.

As loading arbitrary DLLs is a powerful capability a passkey is
added for the new service process host option, and a file containing
valid callers is added with OWNERS from the sandbox to ensure
security review.

A following CL will enable this behavior for screen_ai, but at this
point only tests exercise these APIs

The flow is roughly:
---
In the browser/broker:-

ServiceProcessHost gets a new option:
  .WithPreloadedLibraries

UtilityProcessHost gets a new member:
  preload_libraries_

UtilityProcessHost gives this to the UtilitySandboxedProcessLauncherDelegate

UtilitySandboxedProcessLauncherDelegate turns a list of DLLs into an
opaque blob and attaches it to the sandbox's TargetPolicy during
PreSpawnTarget.

The sandbox smuggles this blob into the target (previous CL).

In the child/target:-

The UtilityMain knows it might have a blob, so asks TargetServices.

UtilityMain coordinates with its sandbox delegate, so knows that
the blob is a pickled list of DLLs.

UtilityMain loads these dlls before sandbox lockdown.
---

Bug: 1435571
Change-Id: Ided63f9d723811b66c183335b5533c84e9783a2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4471953
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1137415}